Abstract

Gasoline compression ignition (GCI) mode engines are characterized by partially premixed charge combustion, leading to significant and simultaneous reductions of nitrogen oxides and particulate matter emissions. However, gasoline compression ignition engine operation suffers from a limited operating window. Air preheating and low-research octane number fuels are required to improve the engine performance. This experimental study used a blend of 70% (v/v) gasoline and 30% diesel as test fuel in a direct injection medium-duty compression ignition engine. Experiments were carried out at 5- and 10-bar brake mean effective pressure (BMEP) engine loads at 1500–2500 rpm engine speeds using a triple injection strategy (two pilots and one main injection) for all test conditions. The combustion phasing was kept constant with respect to crank angle to produce a high power output. The investigations examined engine performance and regulated and unregulated emissions. The test engine was initially operated in conventional diesel combustion mode with diesel for baseline data generation. Gasoline compression ignition mode operation demonstrated a remarkable 16% increase in the brake thermal efficiency and a substantial reduction of 65% in nitrogen oxide emissions compared to the baseline conventional diesel combustion mode. The GCI engine exhaust showed higher concentrations of regulated emissions, namely hydrocarbons and carbon monoxide, and unregulated trace emissions, such as methane, acetylene, toluene, inorganic gaseous species, and unsaturated hydrocarbons.

Graphical Abstract Figure
Graphical Abstract Figure
Close modal

1 Introduction

Consumption of fossil-based energy resources has significantly increased (∼5%) annually in developed nations; hence, there is a growing concern about increasing greenhouse gas emissions [1]. To become fully carbon neutral by 2050, the European Union Parliament aims to reduce the green house gas (GHG) emissions by 55% or more before 2030, vis-à-vis 2020 levels [2]. Internal combustion (IC) engines are the most versatile and reliable machines for energy production and are used in transportation, power generation, industrial, and agricultural applications [3]. Approximately 24% of total carbon dioxide (CO2) emissions globally are contributed by the transport sector [4]. In the transport sector, diesel engines contribute ∼90% of the total oxides of nitrogen (NOx) and particulate matter (PM) [5,6]. Implementing rigorous emission regulations and achieving the proposed carbon-neutrality target require controlling NOx, PM, and CO2 emissions from IC engines [7]. IC engines must be upgraded to improve their power-to-weight ratio, efficiency, and economic feasibility [8]. Advanced combustion techniques, such as reactivity-controlled compression ignition (CI) [9], stratified charge compression ignition, and gasoline compression ignition (GCI), efficiently control combustion and achieve lower emissions [10]. Among advanced combustion techniques, GCI shows excellent potential to enhance combustion performance. Partially or fully electrified vehicles (EVs) co-exist and would continue to do so with diesel and gasoline-fuelled engines. EVs can potentially reduce tailpipe emissions, but their overall GHG impact is at par or more than internal combustion engine vehicles (ICEVs) if the electricity is generated using non-renewable resources. This is in addition to challenges such as the requirement of exotic materials, energy storage systems, and charging infrastructure that must be addressed in totality [11].

GCI engines use less refined fuel, and low fuel injection pressure (FIP) with multiple injections, and offer superior control over the operating range, leading to more efficient combustion [12]. GCI engines reduce the GHG footprint, mitigating the demand for heavily refined fuels [13]. However, GCI engines need improvements in cold starting, combustion noise, cyclic variations, and carbon monoxide (CO) and hydrocarbon (HC) emissions [14]. Various fuel compositions, injection strategies, exhaust gas recirculation (EGR) systems, and engine geometrical modifications need to be explored to overcome these challenges. Studies using GCI engines reported high combustion noise and HC emissions, low soot, and similar efficiency as diesel engines [15]. Partially premixed gasoline–air combustion shows faster fuel–air mixing, advancing the combustion phasing (CA50) [16]. With a double injection strategy, partially premixed combustion (PPC) mode operation exhibited a 50% reduction in NOx emissions compared to a single injection [17]. Changing the pilot injection timing (θPI) from 120 to 20 deg before top dead center (bTDC) in GCI mode showed reduced thermal efficiency and increased NOx and soot [18] due to the formation of locally fuel-rich mixtures [19,20]. Using a triple injection strategy with early pilot injection timing showed an earlier start of combustion (SoC) and increased HC and CO emissions [21]. Increasing second injection fuel mass and advancing second injection timing led to a fuel-lean mixture and reduced smoke [22]. Advancing the timing of the third injection resulted in higher in-cylinder pressure, brake thermal efficiency (BTE), NOx, and very low levels of soot, HC, and CO emissions [23,24]. An increase in the pilot-main interval resulted in elevated brake-specific fuel consumption (FC) due to a delayed CA50. HC and CO emissions increased by 36% and 22% as the FIP varied from 600 to 800 bar [25]. Table 1 summarizes the literature on GCI engine operating conditions and exhaust emissions.

This study examines the impact of triple injection timings on a GCI engine fueled with a low octane number blend of 70% gasoline and 30% (vol.) diesel (G70) operating at 500 bar FIP, at 5- and 10-bar BMEP at 1500–2500 rpm speed. Exhaustive preliminary experiments were conducted to determine the influence of varying fuel injection timings, fuel mass, pilot proportions, EGR rates, and intake air temperatures (IATs) on the GCI combustion. To maintain the desired CA50 without engine knocking, the fuel injection timings, EGR rate, IAT, and fuel quantity were varied for different operating conditions. Engine performance regulated (namely NOx, HC, and CO) and unregulated emissions (12 species) were assessed for GCI combustion and baseline diesel combustion.

2 Experimental Setup and Methodology

The experiment used a turbo-charged four-cylinder, water-cooled, medium-duty diesel engine. Table 2 and Fig. 1 provide the specifications and schematic of the test engine setup, respectively. An eddy current dynamometer (Dynomerk; EC-300) was connected to the engine shaft to control the engine speed/load [28]. The fuel injection system consisted of a fuel filter, high-pressure pump, common rail, and solenoid fuel injector. The coolant and lubricating oil temperatures were maintained at ∼65 °C and ∼80 °C, respectively [28]. Stock electronic control unit (ECU) had engine calibration maps optimized for diesel. An open ECU (MoTeC: M142) with calibrated sensors and actuators was used to develop customized engine maps for the GCI experiments. An open ECU controls the fuel injection timing, pressure, and quantity in the GCI mode. The firing order of cylinders and the reference signal for firing were the same for baseline and GCI modes.

GCI experiments were conducted using G70 test fuel having a research octane number (RON) of ∼70 [29,30]. The physicochemical properties of the constituent fuels can be found in Refs. [31,32]. A U-tube manometer and a laminar flow element (50MC2-2 Meriam) were employed to measure the intake airflow rate. The FC rate was determined by measuring the time taken for 100 ml fuel consumption in a volumetric fuel consumption meter. A certain percentage of uncooled exhaust gas was mixed with boosted intake air before the manifold, and the flow rate of this EGR was measured using an orifice meter and a manometer. K-type thermocouples measured the air and exhaust gas temperatures (EGTs) in the intake manifold and downstream of the turbocharger in the exhaust line.

For measuring the emissions such as NOx, CO, HC, and CO2, a portable gas analyser (HORIBA; MEXA-584L) was used. A lambda module (ETAS; ES635.1) was used to measure the lambda value (λ) of the charge by measuring the presence of oxygen in the exhaust. Unregulated species released by the engine were measured using a Fourier transform infrared-based emission analyser (MEXA-6000FT-E), which could detect up to 32 species in minute quantities [28]. Table 3 shows various instruments and analysers' specifications, accuracy, and uncertainty. For all test conditions, the measurements were conducted after the engine achieved a thermally stable state, and data were acquired four times to ensure repeatability. Then, the average data set was used for calculations.

The maximum BMEP of the engine was 12.5 bar in diesel CI combustion mode. However, the test conditions were well below the maximum BMEP to ensure safety. Experiments were performed at 5- and 10-bar BMEP and 1500, 2000, and 2500 rpm engine speeds. Combustion phasing was maintained between 8 and 11 deg after top dead center (aTDC) to obtain the maximum engine power [33]. Sui et al. [34] maintained the combustion phasing at 8 deg aTDC to ensure higher brake engine efficiency. Reitz and Duraisamy [35] reported that 5 deg aTDC combustion phasing showed higher combustion efficiency for gasoline-like fuels under PPC mode. Too early combustion phasing (near the TDC) could increase the cylinder gas pressure in the compression stroke. Optimum pilot (QPI) and main injection (QMI) mass proportions were determined from the preliminary experiments and the literature (Table 1). For constant QPI1, pilot-1 injection timing sweeps were performed, and it was fixed to 100 deg bTDC to keep the combustion noise below 97 dB level. Furthermore, pilot-2 and main fuel injection timings were varied for all test conditions. 10% and 20% of the total fuel mass were supplied in pilot-1 and pilot-2, respectively. Figure 2 shows the pilot-1 (θPI1), pilot-2 (θPI2), and main injection timings (θMI) at different engine speeds/loads for GCI mode operation in this study. High EGR was supplied at medium engine loads to increase the premixed combustion. However, the EGR rate was reduced at high loads to avoid oxygen deficiency in the cylinder. Turbocharging and hot EGR increased/changed the intake charge temperature, affecting the GCI combustion process.

3 Results and Discussion

The results and discussion are grouped into three sub-sections covering the engine performance characteristics, regulated emission characteristics, and unregulated emission characteristics. These sub-sections include detailed discussions on each variable for GCI mode combustion as per the experimental conditions in Table 2.

3.1 Performance Characteristics.

BTE, EGT, and λ are the performance parameters measured in the GCI and baseline modes.

3.1.1 Brake Thermal Efficiency.

BTE was reduced with increasing engine speed owing to inefficient combustion (Fig. 3). At 5 bar BMEP at 1500 rpm, baseline diesel BTE was ∼30% (∼17% higher than at 2500 rpm), while GCI mode exhibited a 16–25% higher BTE than the baseline. The higher efficiency may be due to optimum combustion phasing. Similarly, GCI mode combustion results in 6–18% and 20–24% higher BTE than the baseline mode combustion at 2000 and 2500 rpm, respectively.

Gasoline improves the fuel spray atomization, and evaporation, thus improving the charge formation more than diesel [36]. BTE consistently decreased with increasing engine speed for both baseline and GCI modes. At 2500 rpm, GCI showed 30–31.5% BTE, which was 4–7% lower than at 1500 rpm. With increasing engine speed, the fuel–air mixing time reduces, and friction losses increase, reducing the BTE [37]. Advanced injection timings (pilot and main) improved the fuel–air mixing, leading to earlier SoC than the retarded injection timings. At 2000 rpm, M4 exhibited 33.54% BTE, while M6 exhibited 30.27%. In-cylinder charge composition, turbulence, and SoC influence the BTE. BTE improved with an engine load increase owing to superior combustion. At high load, 42.88% BTE was observed for H1, which was 14% higher than M1. For GCI mode at 2500 rpm, 10 bar BMEP showed 10–13% lower BTE than 5 bar BMEP, indicating inferior combustion. At 10 bar BMEP, 14–24% and 33–36% higher BTE were achieved for 1500 rpm compared to 2000 and 2500 rpm, respectively. Advanced injection timings (H1, H4, and H7) exhibited 1.6–4% higher BTE than the retarded injection timings in GCI case. GCI demonstrated a superior BTE than baseline, primarily attributable to the combustion phasing.

3.1.2 Exhaust Gas Temperature.

The EGT for baseline diesel and GCI modes is shown in Fig. 4. At 5 bar BMEP at 1500 rpm, the GCI mode exhibited lower (4–6%) EGT than baseline diesel. Leahu et al. [38] stated that EGT decreased as the number of multiple injections. However, 24–30% and 47–70% higher EGT were observed at 2000 and 2500 rpm cases compared to the baseline diesel.

EGT increased with increasing engine speed owing to slightly mixing-controlled combustion. The baseline showed an earlier end of combustion than GCI combustion cases. Hence, large expansion reduced the in-cylinder gas temperature. A higher fuel quantity was burned since a portion of combustion occurred later in the cycle. However, a small late-cycle combustion did not affect the BTE. M1–M3 showed slightly lower EGT than baseline. A total of 14–15% higher EGT were detected for late injection timings than early injection timings at 2000 and 2500 rpm. EGT was higher at peak loads because of higher fuel burning. In contrast, similar EGT was observed for baseline at 5 and 10 bar BMEP, except at 2500 rpm. At BMEP of 10 bar, 34–40%, 47–79% and 28–43% higher EGT were detected in GCI than baseline diesel at 1500, 2000, and 2500 rpm, respectively. Higher main fuel injection quantity and late-cycle combustion increased the EGT, which improved the performance of catalytic converters and soot oxidation catalysts [39].

3.1.3 Lambda.

λ signifies the presence of extra oxygen in the engine cylinder compared to the amount required to achieve stoichiometric combustion. λ > 1.0 indicates a fuel-lean mixture, as shown in Fig. 5.

In baseline diesel, low engine speed showed 40–79% and 4–26% lower λ than higher speeds at 5- and 10-bar BMEP, respectively. For the baseline diesel, λ increased upon increasing the engine speed from 1500 rpm to 2000 rpm. However, it slightly decreased for 2500 rpm compared to 2000 rpm. The stock ECU closed the EGR. Hence, the entire exhaust gas passed through the turbocharger [40]. The boost pressure increased with engine speed due to the turbocharger action, resulting in higher oxygen in the exhaust. Higher engine speed reduced the combustion duration and combustion efficiency, increasing the oxygen in the tailpipe [41]. The boost pressure was not the same for baseline diesel and GCI cases because the turbocharger governed it. Hence, in most cases, λ was lower for GCI mode than baseline due to higher EGR. For GCI mode, 2000 rpm exhibited lower λ than 1500 and 2500 rpm at 5 and 10 bar BMEP. Increasing the engine speed decreased the λ due to higher internal residual gases and lower volumetric efficiency [42]. Reducing the EGR and increasing the fresh charge can increase the λ. However, 2500 rpm engine speed showed 5–21% higher λ than 2000 rpm at 5 bar BMEP. Injection timing's effect on λ was negligible at 1500 and 2500 rpm at 5 bar BMEP. However, λ decreased with retarded injection timings at 2000 rpm. Adjustments were made to the fuel injection mass to ensure the desired engine load at varying injection timings. In addition, the late-cycle combustion could decrease the oxygen in the exhaust gas, resulting in lower λ. At 10 bar BMEP, the baseline diesel exhibited ∼2% and 8–20% higher λ for 1500 and 2500 rpm than its GCI counterpart. No significant differences were observed between H1 to H3 and H4 to H6 cases. Since 2000 rpm is the rated engine speed, it exhibited superior combustion, resulting in lower oxygen in the engine exhaust. At 2500 rpm, no EGR was supplied to avoid oxygen deficiency, resulting in a slight increase (0–13%) in λ than at 2000 rpm (H4–H6).

3.2 Regulated Emission Characteristics.

Regulated emission characteristics mainly included the HC, CO, NO, and CO2 emissions, and the GCI mode was compared to baseline diesel at different engine operating points.

3.2.1 Hydrocarbon Emissions.

GCI mode exhibited higher HC emissions than baseline diesel (Fig. 6) due to fuel vapor trapping in crevices [43]. At 5 bar BMEP at 1500 rpm, the baseline diesel showed 0.525 g/kW h HC emissions, which were reduced by ∼77% at 2500 rpm. Increasing the engine speed increased the in-cylinder temperature due to lower heat losses; therefore, dominant HC oxidation reduced the HC emissions [44].

Compared to baseline diesel, GCI mode at 1500, 2000, and 2500 rpm exhibited 28–144%, 90–137%, and 210–450% higher HC emissions, respectively. Advanced injection timing and higher turbulence caused leaner fuel–air mixture formation. At 2000 rpm engine speed, M5 exhibited ∼33% higher HC emissions than M4. Sometimes, retarded injection causes later SoC and reduced peak combustion temperatures [45]. This could eventually lead to greater HC and CO emissions [19]. The in-cylinder air temperature increased with an engine load increase, improving fuel evaporation. Hence, lower HC emissions were observed at 10 bar BMEP. As the in-cylinder pressure increases during combustion, the expanding gases push the unburned charge into the crevices. As the flames reach the crevices, they may get quenched because crevices have a large surface-to-volume ratio, increasing heat transfer. Pilot injections occur at the beginning of the compression process when the charge temperature and pressure are lower. Original equipment manufacturer (OEM) injectors have a higher spray-included angle; hence, early fuel injection may cause wall impingement of the spray, leading to wall wetting and incomplete combustion. At 10 bar BMEP, GCI mode exhibited 60–125% and 91–198% higher HC emissions than baseline diesel at 1500 and 2000 rpm, respectively. At 2500 rpm, the baseline diesel showed negligible HC emissions, while G70 exhibited 0.22–0.79 g/kW h HC emissions. Despite higher HC, CO emissions, and higher EGT in GCI mode, higher BTE was also observed for GCI mode, owing to superior and optimized combustion phasing. In baseline diesel, attaining combustion phasing closer to the TDC is challenging due to the strong mixing-controlled combustion phase heat release [46].

3.2.2 Carbon Monoxide Emission.

Lower CO emissions were observed in the baseline diesel mode than in the GCI mode (Fig. 7) due to lower diesel volatility, leading to fuel-rich region formation [42]. In addition, the fraction of pilot fuel trapped in the crevice and squish regions underwent incomplete combustion owing to flame quenching (refer to Appendix  1) [12]. The fuel was injected into the piston bowl at the end of the compression stroke in the baseline mode. At 5 bar BMEP at 1500 rpm, 3.65 g/kW h CO emissions were observed, which were ∼67% higher than at 2500 rpm. CO forms during the intermediate combustion reactions of the hydrocarbon fuels, as shown in Eq. (1) [47].
RHRRO2RCHORCOCO
(1)

Increasing in-cylinder temperature and turbulence improves fuel combustion. Unlike baseline diesel, higher CO emissions were observed at higher speeds in GCI mode. The time available for combustion reduced with increasing engine speed, and advanced injection timings increased the fuel in crevice regions, increasing the degree of incomplete combustion [21]. In GCI mode, 130–170% higher CO emissions were observed at 2500 rpm than at 1500 rpm. Higher pilot injection fuel quantity led to localized fuel-lean zone formation, producing CO.

CO emissions from advanced and retarded injection timings depend on CO oxidation and dissociation of CO2. M3 showed 27% lower CO than M1 due to intense PPC. Premixed combustion of M4 exhibited 53% lower CO than M5. At 10 bar BMEP, 0.65–2.82 g/kW h CO emission was observed from baseline diesel, whereas it was an order of magnitude higher up to 76.83 g/kW h in GCI mode. Typically, zones with a lean fuel–air mixture decreased with an increasing engine load, resulting in elevated combustion temperature and lower CO emission. However, dominant lean mixture and late-cycle combustion increase CO emissions [15]. GCI mode exhibited longer late-cycle combustion at full load due to higher fuel quantity and inferior combustion. At 2000 rpm, CO emission reduced by 3–58% than the other two speeds. At higher engine speed, advanced injection timing exhibited high CO emissions than retarded injection timings due to over-leaning of the mixture and lower ignitability of gasoline in GCI mode. Overall, GCI mode exhibited more HC and CO emissions than baseline diesel.

3.2.3 NO Emission.

Figure 8 shows the NO emission from baseline diesel and GCI cases at various test conditions. Diesel predominantly burns in a mixing-controlled combustion phase, increasing the NO formation. At 5 bar BMEP, with increasing engine speed, NO emission increased for the baseline diesel. Baseline diesel at 1500 rpm showed 48% lower NO emission than 2500 rpm. NO emissions were comparable or sufficiently lower for GCI mode than baseline diesel throughout the experimental matrix. In GCI mode, G70 burned in premixed combustion mode at higher λ, resulting in lower NO formation. Equation (2) demonstrates a correlation between the rate of NO formation and the peak combustion temperature [47]:
d[NO]dt=6×1016T1/2exp69,090/T[O2]1/2[N2]
(2)

The combustion temperatures should be below <2200 K to control NO formation [46]. The IAT and hot EGR increase the in-cylinder temperature in GCI mode. Fuel-lean combustion and lower global in-cylinder temperature minimize NO formation. At 1500 rpm, GCI mode exhibited 29–44% higher NO emission than baseline diesel. At 2000 and 2500 rpm in GCI mode, 40–50% lower NO emission was observed than baseline diesel. The local temperature will be higher for baseline diesel mode than GCI modes, increasing the NO emission. The combustion products in the EGR enhance its heat retention, lowering the peak combustion temperature and the NO emissions [48]. The higher latent heat of vaporization of gasoline reduces the charge temperature within the cylinder. At 2000 rpm, GCI mode showed 26–44% and 7–23% lower NO emissions than at 1500 and 2500 rpm, respectively. At BMEP of 5 bar, variations in the GCI mode fuel injection timings led to 0.8–19% variations in NO. Late injection timings showed higher or comparable NO emissions for all conditions than earlier injections due to the less time available for mixing and increased local equivalence ratio. This led to higher localized temperatures and, hence, higher NO emissions. For baseline diesel at 10 bar BMEP, NO emission was reduced with a increasing engine speed. At BMEP of 10 bar, GCI mode showed lower NO emission than the baseline diesel. With increased engine load, GCI mode exhibited dominantly premixed combustion [49]. In GCI mode, NO emission increased with engine speed due to dominant mixing-controlled combustion, which had localized high-temperature zones where NO formed. GCI mode showed 60–86% higher NO emission at 2500 rpm than 1500 rpm. Advanced injection timings resulted in 24–32% higher NO emission than retarded injection timings [50].

3.2.4 Carbon Dioxide Emissions.

The baseline diesel showed a lower CO2 emission than GCI mode, as shown in Fig. 9. Sellnau et al. [51] reported 14.4% lower indicated specific CO2 emission for the GCI mode than baseline diesel at 1500 rpm. With increasing engine speed and injection pulse duration, CO2 emission showed increasing and decreasing trends, respectively, as reported by Syafiq et al. [52]. Higher engine loads exhibited higher CO2 emission due to more fuel burning [53].

3.3 Unregulated Emission Characteristics.

Diesel engines emit several unregulated emission species [54]. These are sub-categorized into (a) discrete oxides of nitrogen (N2O and NO2), (b) saturated hydrocarbons (CH4 and C8H18), (c) unsaturated hydrocarbons (C2H6 and C6H6), and (d) inorganic and organic gaseous species (SO2 and HCHO).

3.3.1 Nitrogen Oxide.

Gasoline-fuelled engines show minimal NO2/NO ratio than diesel-fuelled engines. The NO to NO2 conversion happens in the flame zones via reactions given in Eqs. (3) and (4) [47].
NO+RO2NO2+RO
(3)
NO+OH+O2HNO2+O2NO2+HO2
(4)

Here, R represents a hydrocarbon radical or a hydrogen atom. Higher RO2 concentration is produced in the cooler regions of the flame. Subsequently, NO2 is converted to NO via (NO2+ONO+O2) reaction, unless NO2 formed in flames is quenched by a cooler fluid [55]. At medium combustion temperatures, N2O showed a particular share in the NOx formation [56].

Rößler et al. [57] reported a higher NO2 concentration whenever large quantities of NOx are formed under higher λ conditions. In line with their study, 62–77% higher NO2 was observed in baseline diesel than in GCI mode, as shown in Fig. 10. At 1500 rpm, baseline diesel showed 50% higher NO2 than at 2500 rpm. The NO2 to NO conversion becomes stronger as higher charge turbulence quenches the high-temperature flames. Higher engine speeds showed 70–90% lower NO2 for GCI than baseline cases. At BMEP of 5 bar, advanced injection timings exhibited 10–143% higher NO2 emissions than retarded injection timings. Two to six times lower NO2 emissions were detected at higher engine loads than medium loads. The net NO2 emission formation reduced with increasing NO conversion and deficiency in available oxygen. At 2000 rpm, GCI mode showed ∼15 times lower NO2 than baseline diesel. At 2500 rpm, GCI mode exhibited negligible NO2 while the baseline diesel showed ∼4 ppm, which is also very low.

3.3.2 Sulfur Dioxide.

The SO2 formation relies on the traces of fuel's sulfur. Lin et al. [58] reported that even the slightest of excess air in the exhaust could increase SO2. Figure 4 shows that the EGT raised with engine loads/speeds owing to prolonged combustion. Late-cycle combustion oxidizes partially burnt species, accelerating the formation of CO2, SO2, etc. in the exhaust.

At 5 bar BMEP, SO2 concentration increased with engine speed, and it decreased at 10 bar BMEP, as shown in Fig. 11. For the baseline diesel, SO2 emissions increased by 18% while changing the engine speed from 1500 to 2500 rpm. Similarly, in GCI mode, 13–42% higher SO2 was detected at 2500 rpm than at 1500 rpm. Obeid et al. [59] reported that fuel sulfur and engine load influenced SO2 formation. At BMEP of 10 bar, 3–50% lower SO2 was detected than 5 bar BMEP due to SO2 oxidation. Elevated in-cylinder temperatures helped the SO2 oxidation via Eqs. (5) and (6) and formed gas-phase SO3 [60].
SO2+O+(M)SO3+(M)
(5)
SO2+OHSO3+H
(6)

At 10 bar BMEP, the baseline diesel showed a 20% reduction in SO2 when increasing the engine speed from 1500 to 2500 rpm. However, this reduction became 140–160% for GCI mode during the engine speed sweep.

3.3.3 Formaldehyde.

Relatively lower formaldehyde (HCHO) traces were detected in baseline diesel than in GCI cases, as shown in Fig. 12. The crevices are a primary source of HCHO due to flame quenching [61]. HCHO is a relatively unstable species in high-temperature conditions (>1100 K) [62].
HCHO+OHHCO+H2O
(7)
O2+HCOHO2+CO
(8)
HCO+(M)CO+(M)+H
(9)

Oxidation of HCHO occurs faster <950 K than CH4 and C2H6 [63], as shown in Eqs. (7)(9). HCHO oxidation is significantly faster at temperatures above 1500 K. Typically, HCHO is consumed rapidly when the OH, H, and O radicals form and disappear before this pool's peak is reached [64]. HCHO traces decrease with increasing mixture dilution and consequently decreasing flame temperatures [61]. Higher HCHO (∼74%) traces were observed at 1500 rpm than at 2500 rpm for baseline diesel. Higher engine speed increased the charge turbulence, forming a leaner mixture. In GCI combustion mode at 5 bar BMEP, ∼40% lower HCHO was observed at 2500 rpm than at 1500 rpm. M3 showed 195% higher HCHO than M1, whereas M9 exhibited 34% higher HCHO than M7. HCHO traces and other partial oxidation products may survive through the expansion stroke due to the quick cooling of in-cylinder gases. At 2000 rpm, lower HCHO trace concentrations were seen than at the two other engine speeds. HCHO forms in the areas between the wall and flames before quenching [63]. Higher engine loads enhance the formation of hot products, increasing the possibility of HCHO oxidation. For baseline diesel at 10 bar BMEP, 7–24% lower HCHO traces were observed than at 5 bar BMEP. However, 1–63% higher HCHO was noticed for GCI mode due to low-temperature combustion (LTC) [61]. With increasing pilot fuel quantity, HCHO originated in the crevice gases also increased. At 10 bar BMEP, 2000 rpm engine speed exhibited 42–50% and 27–38% lower trace HCHO emissions than 1500 rpm and 2500 rpm, respectively. Depending on the temperature and exhaust gas composition, HCHO is also formed or destroyed in the exhaust system [60].

3.3.4 HNCO.

The exhaust's nitrogen oxides and certain organic compounds primarily govern isocyanic acid (HNCO) formation.

HNCO and NH3 are among the toxic compounds released by vehicles, and their formation is given by the reactions shown in Eqs. (10)(12) [65]. The reactions of NCO groups with adsorbed H forms the HNCO.
2NO+5CO+H2O2HNCO+3CO2
(10)
CO(NH2)2NH3+HNCO
(11)
2HNCO+H2ONH3+CO2
(12)

In baseline diesel, 1500 rpm engine speed showed 34–41% higher HNCO trace emission than higher engine speeds (Fig. 13). Increasing the speed reduced the HNCO owing to a rise in local in-cylinder temperature. Devolatilization of fuel forms HCN, which tends to formation of NCO and N2O [56]. NCO reaction with H2O and H2 can lead to the formation of HNCO. Prolonged fuel-rich combustion (λ < 1) results in higher HNCO and NH3 formation [65]. GCI mode exhibited 5–200% higher HNCO emissions than baseline diesel mode. High CO emission from the GCI mode engine caused higher HNCO formation, while its oxidation improved with radicals such as H, OH, and O [56]. Advanced fuel injection timings showed 7–41% higher HNCO emissions than late injection. Early fuel injection timings produced large pyrolysis fuel products from the lean fuel–air mixture. During idling, HNCO and its precursor were <0.2% and 1% of the total hydrocarbons [66]. OH radicals exposed to precursors of HNCO were too small to control HNCO emissions in diesel engines [66]. In baseline diesel, 10 bar BMEP showed higher HNCO emissions than 5 bar BMEP, whereas it was lower in GCI mode. For higher engine speeds, 56–87% lower HNCO was detected at BMEP of 10 bar than at 5 bar. The HNCO formation reduces with reduced oxygen concentration, the presence of fuel nitrogen, and increased peak combustion temperature [67].

3.3.5 Methane (CH4).

Diesel engines emit negligible trace CH4 emissions. With increasing engine speed, CH4 trace emissions increased at mid and high engine loads. At 5 bar BMEP at 2500 rpm, 12–26% higher CH4 traces were observed than at 1500 rpm. CH4 trace concentration supports intermediate species formation, thereby increasing the polycyclic aromatic hydrocarbon (PAH) formation [68]. Fuel-rich combustion forms higher traces of CH4 and C2H2, which increases the trace PAH formation (Fig. 14).

At 10 bar BMEP at 1500 rpm, 20–40 ppm CH4 was measured, but it was <2 ppm at 5 bar BMEP. 10 bar BMEP at 2500 rpm exhibited ∼160–210 ppm CH4 which was 5–11 times higher than 5 bar BMEP. Dissociation of the C–C bonds in the combustion products could form CH4 and C2H6. Gas-phase CH3 and C2H5 radicals react with H, H2, –OH, or other radicals forming CH4 and C2H6 [69]. Gasoline combustion leads to higher methyl and ethyl radical formation than baseline diesel combustion [70]. The methyl radical reacts with a H by radical recombination, yielding CH4.

3.3.6 Ethane (C2H6).

Figure 15 shows that baseline diesel emitted negligible traces of C2H6 for both engine loads. In the hierarchical structure of the hydrocarbon fuel oxidation mechanisms, C2H6 oxidation plays a vital role [71]. Premixed combustion of G70 causes significant intermediate temperature regimes, resulting in C2H6 emissions. Higher in-cylinder temperature, hydroxyl radicals, and lower flame quenching reduce the C2H6 traces in the exhaust.

In GCI mode, 2000 rpm engine speed exhibited 54–60% and 46–68% lower C2H6 than at 1500 and 2500 rpm, respectively. Birkavs and Smigins [72] reported that gasoline engines emitted 15–23 ppm C2H6 and 130–170 ppm CH4. Advanced injection timings led to higher emissions of C2H6 than retarded injection timings at medium loads due to fuel-lean conditions. Retarded fuel injection timings at full loads possibly form fuel-rich regions. Therefore, reduced C2H6 traces were observed at high loads. At 10 bar BMEP at 1500 rpm, ∼15 ppm C2H6 was observed, which was 72–94% higher than at 2500 rpm. The radicals such as H,OH,HO2, and CH3 oxidize C2H6 through the hydrogen abstraction mechanism [73].

3.3.7 Acetylene (C2H2).

Diesel combustion emits low (<3 ppm) C2H2 till 6 bar BMEP [74]. In high combustion temperatures (>1200 K), C2H2 forms from the large and small hydrocarbons, alkanes, alkenes, and aromatics [39]. At high combustion temperatures, the formation of C2H2 was dominated by the formation of PAHs [75]. Diesel is a mixture of heavy hydrocarbons, and its combustion generates C2H2 along with other species, as shown by Eq. (13) [75].
xC16H3434aH2+16bC10H8+16cCH4+16dC2H4+16eC2H2
(13)

GCI mode exhibited lower trace concentrations of C2H2 (<2 ppm) at 1500 and 2000 rpm engine speeds at BMEP of 5 bar (Fig. 16). M9 exhibited 58% higher C2H2 traces than M7 due to predominantly mixing-controlled combustion. This suggested a greater soot formation in GCI mode than baseline diesel mode. 10 bar BMEP exhibited a higher C2H2 trace concentrations than 5 bar BMEP due to fuel-rich combustion [76]. Residence time, available oxygen, and CxHy radicals determine the C2H2 oxidation and decomposition in the engine cylinder [77]. At 10 bar BMEP at 1500 rpm, 2–31 times higher traces of C2H2 were observed than at 5 bar BMEP. Similarly, with increasing engine loads, 4.75–13.8 and 2.9–7.67 times higher trace C2H2 were observed at 2000 and 2500 rpm, respectively. At 10 bar BMEP, retarded injection timings exhibited 8–760% higher C2H2 than advanced injection timings. C2H2 reacts with O2, O, and OH radicals producing CO2, H2O, and other intermediate species [78]. Hence, a deficiency in local oxygen availability reduces the C2H2 oxidation, thus increasing C2H2 trace emissions. Fuel-rich (λ < 0.4) and high-temperature (>2000 K) combustion environment triggers the C2H2 formation in the engine combustion chamber [79].

3.3.8 Ethylene (C2H4).

Lower trace C2H4 concentrations were observed for baseline diesel than the GCI mode, as shown in Fig. 17. Gas-phase fuel molecules undergo thermal cracking and produce traces of C2H4 [80]. At 5 bar BMEP, 57–64% lower C2H4 traces were detected at 2500 rpm than at 1500 rpm.

In GCI mode, 2000 rpm exhibited 87–95% lower C2H4 trace concentration than other engine speeds. M2 and M8 showed lower C2H4 than other GCI mode cases, indicating that intermediate fuel injection timings reduced the trace concentration of C2H4 in the exhaust. Unlike 5 bar BMEP, C2H4 due to higher fuel cracking, trace concentrations increased with engine speed at 10 bar BMEP for baseline diesel. At BMEP of 10 bar at 1500 and 2000 rpm, 5–58% and 74–87% higher C2H4 were found than 5 bar BMEP. At higher engine loads, advanced fuel injection timings led to lower trace concentrations of C2H4 than retarded injection timings.

3.3.9 Benzene (C6H6).

Benzene (C6H6) is a soot precursor and carcinogenic species [74]. At mid and high loads, the C6H6 traces are reduced with increasing engine speed (1600–200 rpm) [81]. In this study, at 5 bar BMEP, GCI mode exhibited 1.2–7.5 times higher C6H6 emissions than baseline diesel (Fig. 18). Retarded fuel injection timings showed 13–54% lower C6H6 trace concentrations than advanced injection timings. A total of 1300–1700 K combustion temperatures with fuel-rich regions in the engine combustion chamber yield large trace concentrations of C6H6 [79].

At 5 and 10 bar BMEPs, 2000 rpm exhibited 44–74% and 67–82% lower C6H6 trace emissions than other engine speeds of 1500 and 2500 rpm, respectively. For GCI mode, 14–74% higher C6H6 trace concentrations were observed at 10 bar BMEP rather than 5 bar BMEP. Pyrolysis of fuel and lubricating oil at elevated temperatures and pressures promote the formation of C6H6 in the engine combustion chamber [82]. At 10 bar BMEP, the retarded injection timings exhibited 19–55% higher C6H6 trace concentrations than advanced injection timings. Ruan et al. [83] reported that higher combustion temperatures promote oxidation/destruction of traces of C6H6.

3.3.10 C7H8 Aromatic Hydrocarbons.

The C7H8 primarily refers to toluene. However, C7H8 could represent other hydrocarbons apart from toluene. The molecular formula C7H8 represents a group of compounds known as aromatic hydrocarbons. Other aromatic hydrocarbons could also have this formula [84,85], for instance, xylene isomers, ethylbenzene, and styrene. These compounds have similar molecular formulas but different structures and properties.

The reaction of benzene with a –CH3 radical forms monosubstituted benzene hydrocarbons (C7H8) [86]. Baseline diesel emitted <6 ppm C7H8 concentration, whereas GCI mode exhibited up to 72 ppm trace concentration of C7H8 (Fig. 19). Platt et al. [87] revealed that gasoline vehicles produced large concentrations of C7H8 than modern diesel engines. At 5 bar BMEP at 1500, 2000, and 2500 rpm, 12–14, 6–7, and 7–12 times higher C7H8 concentrations were observed in GCI mode compared to baseline diesel mode. Advanced fuel injection timings showed 12–34% higher trace emissions of C7H8 than retarded injection timings. Slightly higher and 57–93% lower C7H8 trace concentrations were seen for baseline diesel and GCI modes at BMEP of 10 and 5 bar, respectively. Puškár et al. [88] reported that trace concentrations of C7H8 diminished with increasing load. At BMEP of 10 bar at 2000 and 2500 rpm engine speed, almost similar C7H8 trace concentrations were observed for baseline diesel and GCI modes.

3.3.11 Octanes (C8H18).

The C8H18 represents a group of hydrocarbons known as alkanes or, more commonly, octanes [89]. In the context of hydrocarbons, C8H18 can be collectively referred to as “octanes.” This group includes various isomers of octane, such as n-octane and branched isomers, like iso-octane, 2-methyl heptane, 3-methyl heptane, and so on [90].

Lower engine loads exhibited higher octanes (normal and isomers) trace concentration than higher engine loads, similar to the observations made by Agarwal et al. [91]. The baseline diesel exhibited 25–89% lower C8H18 trace emissions than GCI mode (Fig. 20). Gasoline contains compounds with carbon chains in the range of C7C11, whereas they are in the range of C13C18 for diesel [92]. Hence, unburned gasoline results in higher C8H18 trace emissions than its diesel counterpart [39]. For the baseline diesel, 2500 rpm engine speed exhibited ∼40% lower C8H18 than at 1500 rpm. Increasing the engine speed reduced the C8H18 trace concentrations, owing to elevated in-cylinder temperature. In contrast, at 2500 rpm, GCI mode showed higher trace concentrations of C8H18 than 1500 rpm due to incomplete combustion [47]. 10 bar BMEP exhibited 6–40% lower C8H18 trace concentrations than 5 bar BMEP [76].

3.4 Comparison of Results From the Literature.

This section compares the findings of this work with similar studies in the open literature to detect agreements and differences. The triple injection strategy showed higher HC and CO emissions, as reported by An et al. [25]. Higher engine loads showed higher BTE, EGT, and NOx emissions than lower ones. Similar results were reported by Agarwal et al. [26,27]. However, in contrast to results reported by Agarwal et al. [26,27], the CO emission increased with increasing engine load. Advanced SoMI timing exhibited higher BTE, HC, and CO emissions than the retarded one, except for some conditions, which were in contrast to Ref. [26]. Agarwal et al. [27] reported that retarded SoMI timing exhibited higher BTE and NOx and lower HC and CO emissions than advanced SoMI timings. These observations were not verified in this study. However, the EGT was higher for retarded SoMI timings, which was in agreement with Ref. [27].

In contrast to results reported by Cung et al. [18] and Cung and Ciatti [19], retarded pilot injection timings showed lower BTE and NOx emissions. EGT increased, and HC and CO emissions decreased with retarded pilot injection timings. They coincide with results reported by Cung et al. [18], Cung and Ciatti [19], and Zyada et al. [23]. In this study, the pilot-2 fuel proportion was kept at 20%, because it exhibited higher BTE than 10% pilot-2 fuel mass, as reported by Liu et al. [22]. Increasing the interval between the pilot-2 and main injection timings decreased the BTE, as also reported by Liu et al. [24]. Lambda and unregulated emissions were not reported in the available open literature. Hence, the results of this study are largely in line with the results of previous studies in the open literature. The test results depend on factors such as fuel, engine geometry, test conditions, operating mode, etc. Variations in these parameters could cause deviations in the output parameters. This study is valid for medium-duty diesel engines operated in GCI combustion mode using gasoline-diesel blends.

4 Conclusions

This experimental study investigated the feasibility of a low octane fuel (G70) powered CI engine in GCI mode, ranging from medium- to high loads and variable speeds and compared it with baseline diesel mode. GCI combustion was achieved for a range of engine speed (1500–2500 rpm) and engine load (5–10 bar BMEP) without major retrofitment. The fuel injection strategy was tuned per the engine speed and load.

  • GCI showed up to 6% higher BTE than baseline diesel, which is a significant improvement. BTE consistently decreased with increasing engine speed for baseline diesel and GCI modes. Advanced injection timings showed higher BTE than retarded ones. GCI mode did not deliver significant benefits at higher engine speeds/loads.

  • GCI mode exhibited 24–79% higher EGT and 40–66% lower NO emission than baseline diesel. GCI mode led to higher CO and HC (28–144%) emissions than baseline diesel. CO emission concentrations were significantly higher at a BMEP of 10 bar than at 5 bar in GCI mode.

  • GCI mode emitted 62–90% lower NO2 trace concentrations than baseline diesel. Increasing engine speed and retarding injection timings reduced NO2 trace emission. HCHO trace emission concentrations were higher in GCI mode than in baseline diesel. The rated engine speed of 2000 rpm exhibited lower HCHO trace emissions than other speeds.

  • Methane, acetylene, and benzene trace emission concentrations were higher in GCI mode at higher engine loads. However, medium engine loads showed higher toluene and n-octane trace emission concentrations.

This experimental study demonstrated that medium-duty diesel engines could function effectively in GCI mode by optimizing the fuel injection strategy and appropriate intake charge conditioning. Modifications in the piston shape/profile and injector design alternations may be required to control unburned and partially burned species emissions.

Acknowledgment

The authors express gratitude for the support of the Science and Engineering Research Board (SERB), Government of India (Grant SERB/ME/2021403) for undertaking this study. Sir J C Bose Fellowship (Grant EMR/2019/000920) and the SBI endowed Chair Professorship from the State Bank of India to Professor Avinash Kumar Agarwal are also acknowledged. Under the National Postdoctoral Fellowship scheme, financial assistance from SERB to Dr. M. Krishnamoorthi (PDF/2021/001209) is also appreciated. Special thanks to Roshan Lal, Hemant Kumar, Surendra, and the Engine Research Laboratory team for their assistance in conducting these time-bound experiments. The authors also acknowledge Ms. Utkarsha Sonawane and Sh. Sam Joe, for their assistance in preparing this manuscript.

Conflict of Interest

There are no conflicts of interest. This article does not include research in which human participants were involved. Informed consent not applicable. This article does not include any research in which animal participants were involved.

Data Availability Statement

The datasets generated and supporting the findings of this article are obtainable from the corresponding author upon reasonable request.

Appendix 1

In GCI mode, CO emissions increased with increasing pilot fuel quantity. The pilot fuel mass saw an augmentation with increasing engine load and speed. Despite the elevated in-cylinder temperatures associated with high engine loads, incomplete combustion of fuel parcels trapped in crevices occurred. Oxidation of CO to CO2 depends on the availability of oxidants, peak temperature, and residence time. In addition, inferior spray atomization, inadequate fuel–air mixing, and insufficient time for completion of combustion resulted in CO formation.

References

1.
Workman
,
D.
,
2021
, “
Crude Oil Imports by Country
,”
World Top Exports 2021.
https://www.worldstopexports.com/crude-oil-imports-by-country/, Accessed October 7, 2022.
2.
Commission of the European Union Parliament
,
2020
, “
Stepping Up Europe’s 2030 Climate Ambition
,”
Off J Eur Union Brussels 2020
. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:52020DC0562, Accessed October 8, 2020.
3.
Bartolucci
,
L.
,
Cordiner
,
S.
,
Mulone
,
V.
,
Krishnan
,
S. R.
, and
Srinivasan
,
K. K.
,
2021
, “
A Computational Investigation of the Impact of Multiple Injection Strategies on Combustion Efficiency in Diesel–Natural Gas Dual-Fuel Low-Temperature Combustion Engines
,”
ASME J. Energy Resour. Technol.
,
143
(
2
), p.
022305
.
4.
IEA
,
2022
, “Transport: Improving the Sustainability of Passenger and Freight Transport,” https://www.iea.org/topics/transport, Accessed October 8, 2022.
5.
Su
,
X.
,
Chen
,
H.
,
Gao
,
N.
,
Ding
,
M.
,
Wang
,
X.
,
Xu
,
H.
, and
Zhang
,
P.
,
2023
, “
Combustion and Emission Characteristics of Diesel Engine Fueled With Diesel/Cyclohexanol Blend Fuels Under Different Exhaust Gas Recirculation Ratios and Injection Timings
,”
Fuel
,
332
, p.
125986
.
6.
Bai
,
Y.
,
Lan
,
Q.
,
Fan
,
L.
,
Yao
,
J.
,
Kong
,
X.
,
Yang
,
L.
, and
Wen
,
L.
,
2023
, “
Pressure Characteristics of the Fuel System for Two-Stroke Diesel Engines Under Different Operational Modes
,”
Fuel
,
332
, p.
126007
.
7.
Reitz
,
R. D.
,
Ogawa
,
H.
,
Payri
,
R.
,
Fansler
,
T.
,
Kokjohn
,
S.
,
Moriyoshi
,
Y.
,
Agarwal
,
A. K.
, et al
,
2020
, “
IJER Editorial: The Future of the Internal Combustion Engine
,”
Int. J. Engine Res.
,
21
(
1
), pp.
3
10
.
8.
Wen
,
M.
,
Liu
,
H.
,
Cui
,
Y.
,
Ming
,
Z.
,
Feng
,
L.
, and
Yao
,
M.
,
2023
, “
Optical Diagnostics of Methanol Active-Thermal Atmosphere Combustion in Compression Ignition Engine
,”
Fuel
,
332
, p.
126036
.
9.
Curran
,
S.
,
Hanson
,
R.
,
Wagner
,
R.
, and
Reitz
,
R. D.
,
2013
, “Efficiency and Emissions Mapping of RCCI in a Light-Duty Diesel Engine,” SAE Tech. Pap., 2.
10.
Qiao
,
J.
,
Liu
,
J.
,
Zhang
,
Q.
,
Liang
,
J.
,
Wang
,
R.
,
Zhao
,
Y.
, and
Shen
,
D.
,
2023
, “
Experimental Investigation on the Effects of Miller Cycle Coupled With Asynchronous Intake Valves on the Performance of a High Compression Ratio GDI Engine
,”
Fuel
,
332
, p.
126088
.
11.
Goel
,
S.
,
Sharma
,
R.
, and
Rathore
,
A. K.
,
2021
, “
A Review on Barrier and Challenges of Electric Vehicle in India and Vehicle to Grid Optimisation
,”
Transp. Eng.
,
4
, p.
100057
.
12.
Krishnamoorthi
,
M.
, and
Agarwal
,
A. K.
,
2023
, “
Numerical Simulation and Emissions Performance of a Gasoline Compression Ignition Engine at High Idle and Low-Load Conditions
,”
IFToMM WC2023
,
Tokyo, Japan
,
Nov. 5–10
, pp.
992
1001
.
13.
Kalghatgi
,
G.
, and
Johansson
,
B.
,
2018
, “
Gasoline Compression Ignition Approach to Efficient, Clean and Affordable Future Engines
,”
Proc. Inst. Mech. Eng. Part D J. Automob. Eng.
,
232
(
1
), pp.
118
138
.
14.
Zhang
,
Y.
,
Kumar
,
P.
,
Tang
,
M.
,
Pei
,
Y.
,
Merritt
,
B.
,
Traver
,
M.
, and
Popuri
,
S.
,
2020
, “
Impact of Geometric Compression Ratio and Variable Valve Actuation on Gasoline Compression Ignition in a Heavy-Duty Diesel Engine
,”
ASME 2020 Internal Combustion Engine Fall Technical Conference
,
Virtual
,
Nov. 4–6
.
15.
Cung
,
K.
,
Moiz
,
A.
,
Smith
,
E. M.
,
Bitsis
,
D. C.
,
Michlberger
,
A.
,
Briggs
,
T.
, and
Miwa
,
J.
,
2021
, “
Gasoline Compression Ignition (GCI) Combustion of Pump-Grade Gasoline Fuel Under High Compression Ratio Diesel Engine
,”
Transp. Eng.
,
4
, p.
100066
.
16.
Goyal
,
H.
, and
Kook
,
S.
,
2019
, “
Ignition Process of Gasoline Compression Ignition (GCI) Combustion in a Small-Bore Optical Engine
,”
Fuel
,
256
, p.
115844
.
17.
Kim
,
D.
, and
Bae
,
C.
,
2017
, “
Application of Double-Injection Strategy on Gasoline Compression Ignition Engine Under Low Load Condition
,”
Fuel
,
203
, pp.
792
801
.
18.
Cung
,
K.
,
Bitsis
,
D. C.
,
Miwa
,
J.
,
Smith
,
E.
,
Briggs
,
T.
,
Morris
,
A.
,
Michlberger
,
A.
, and
Moiz
,
A. A.
,
2021
, “Investigation of Gasoline Compression Ignition (GCI) Combustion in a High Compression Ratio Heavy Duty Single Cylinder Diesel Engine,” SAE Tech Pap.
19.
Cung
,
K.
, and
Ciatti
,
S.
,
2017
, “
A Study of Injection Strategy to Achieve High Load Points for Gasoline Compression Ignition (GCI) Operation
,”
Vol. 1 Large Bore Engines; Fuels; Adv. Combust.
,
Seattle, WA
,
Oct. 15–18.
20.
Kobashi
,
Y.
,
Wang
,
Y.
,
Shibata
,
G.
,
Ogawa
,
H.
, and
Naganuma
,
K.
,
2019
, “
Ignition Control in a Gasoline Compression Ignition Engine With Ozone Addition Combined With a Two-Stage Direct-Injection Strategy
,”
Fuel
,
249
, pp.
154
160
.
21.
Wang
,
B.
,
Pamminger
,
M.
,
Vojtech
,
R.
, and
Wallner
,
T.
,
2020
, “
Impact of Injection Strategies on Combustion Characteristics, Efficiency and Emissions of Gasoline Compression Ignition Operation in a Heavy-Duty Multi-cylinder Engine
,”
Int. J. Engine Res.
,
21
(
8
), pp.
1426
1440
.
22.
Liu
,
X.
,
Goyal
,
H.
,
Kook
,
S.
, and
Ikeda
,
Y.
,
2019
, “
Triple Injection Strategies for Gasoline Compression Ignition (GCI) Combustion in a Single-Cylinder Small-Bore Common-Rail Diesel Engine
,”
Detroit, MI
, SAE Technical Paper 2019-01-1148.
23.
Zyada
,
A.
,
Zoldak
,
P.
, and
Naber
,
J.
,
2022
, “
Development of Multiple Injection Strategy for Gasoline Compression Ignition High Performance and Low Emissions in a Light Duty Engine
,”
Detroit, MI
, SAE Technical Paper 2022-01-0457.
24.
Liu
,
J.
,
Wang
,
H.
,
Zheng
,
Z.
,
Li
,
L.
,
Mao
,
B.
,
Xia
,
M.
, and
Yao
,
M.
,
2018
, “
Improvement of High Load Performance in Gasoline Compression Ignition Engine With PODE and Multiple-Injection Strategy
,”
Fuel
,
234
, pp.
1459
1468
.
25.
An
,
Y.
,
Tang
,
Q.
,
Vallinayagam
,
R.
,
Shi
,
H.
,
Sim
,
J.
,
Chang
,
J.
,
Magnotti
,
G.
, and
Johansson
,
B.
,
2019
, “
Combustion Stability Study of Partially Premixed Combustion by High-Pressure Multiple Injections With Low-Octane Fuel
,”
Appl. Energy
,
248
, pp.
626
639
.
26.
Agarwal
,
A. K.
,
Solanki
,
V. S.
, and
Krishnamoorthi
,
M.
,
2023
, “
Experimental Evaluation of Pilot and Main Injection Strategies on Gasoline Compression Ignition Engine—Part 2: Performance and Emissions Characteristics
,”
SAE Int. J. Engines
,
16
(
6
), pp.
833
852
.
27.
Agarwal
,
A. K.
,
Solanki
,
V. S.
, and
Krishnamoorthi
,
M.
,
2023
, “
Gasoline Compression Ignition (GCI) Combustion in a Light-Duty Engine Using Double Injection Strategy
,”
Appl. Therm. Eng.
,
223
, p.
120006
.
28.
Kumar
,
V.
,
Singh
,
A. P.
, and
Agarwal
,
A. K.
,
2020
, “
Gaseous Emissions (Regulated and Unregulated) and Particulate Characteristics of a Medium-Duty CRDI Transportation Diesel Engine Fueled With Diesel-Alcohol Blends
,”
Fuel
,
278
, p.
118269
.
29.
Bakker
,
P. C.
,
De Abreu Goes
,
J. E.
,
Somers
,
L. M. T.
, and
Johansson
,
B. H.
,
2014
, “Characterization of Low Load PPC Operation Using RON70 Fuels,” SAE Technical Papers.
30.
Agarwal
,
A. K.
,
Krishnamoorthi
,
M.
, and
Singh
,
H.
,
2024
, “
Macroscopic and Microscopic Spray Characterisation of Low-Octane Blends for Gasoline Compression Ignition Engines
,”
Fuel
,
361
, p.
130346
.
31.
Kabil
,
I.
,
Sim
,
J.
,
Badra
,
J. A.
,
Eldrainy
,
Y.
,
Abdelghaffar
,
W.
,
Mubarak Ali
,
M. J.
,
Ahmed
,
A.
,
Sarathy
,
S. M.
,
Im
,
H. G.
, and
Elwardany
,
A.
,
2018
, “
A Surrogate Fuel Formulation to Characterize Heating and Evaporation of Light Naphtha Droplets
,”
Combust. Sci. Technol.
,
190
(
7
), pp.
1218
1231
.
32.
Parveg
,
A. S. M. S.
, and
Ratner
,
A.
,
2023
, “
Droplets Combustion Characteristics Comparison of Single Component and Multicomponent Diesel Surrogates With Petroleum-Based Commercial Diesel Fuel
,”
Vol. 7 Energy
,
New Orleans, LA
,
Oct. 29–Nov. 2
.
33.
Caton
,
J. A.
,
2014
, “
Combustion Phasing for Maximum Efficiency for Conventional and High-Efficiency Engines
,”
Energy Convers. Manage.
,
77
, pp.
564
576
.
34.
Sui
,
W.
,
Hall
,
C. M.
, and
Kapadia
,
G.
,
2020
, “
Cylinder-Specific Model-Based Control of Combustion Phasing for Multiple-Cylinder Diesel Engines Operating With High Dilution and Boost Levels
,”
Int. J. Engine Res.
,
21
(
7
), pp.
1231
1250
.
35.
Reitz
,
R. D.
, and
Duraisamy
,
G.
,
2015
, “
Review of High Efficiency and Clean Reactivity Controlled Compression Ignition (RCCI) Combustion in Internal Combustion Engines
,”
Prog. Energy Combust. Sci.
,
46
, pp.
12
71
.
36.
Zhang
,
Z.
,
Li
,
J.
,
Tian
,
J.
,
Xie
,
G.
,
Tan
,
D.
,
Qin
,
B.
,
Huang
,
Y.
, and
Cui
,
S.
,
2021
, “
Effects of Different Diesel-Ethanol Dual Fuel Ratio on Performance and Emission Characteristics of Diesel Engine
,”
Processes
,
9
(
7
), p.
1135
.
37.
Teoh
,
Y. H.
,
Masjuki
,
H. H.
,
Kalam
,
M. A.
, and
How
,
H. G.
,
2015
, “
Comparative Assessment of Performance, Emissions and Combustion Characteristics of Gasoline/Diesel and Gasoline/Biodiesel in a Dual-Fuel Engine
,”
RSC Adv.
,
5
, pp.
71608
71619
.
38.
Leahu
,
C. I.
,
Tarulescu
,
S.
, and
Tarulescu
,
R.
,
2018
, “
The Exhaust Gas Temperature Control Through an Adequate Thermal Management of the Engine
,”
IOP Conf. Ser.: Mater. Sci. Eng.
,
444
, p.
072016
.
39.
Agarwal
,
A. K.
, and
Krishnamoorthi
,
M.
,
2022
, “
Review of Morphological and Chemical Characteristics of Particulates From Compression Ignition Engines
,”
Int. J. Engine Res.
,
24
(
7
), pp.
2807
2865
.
40.
Galindo
,
J.
,
Dolz
,
V.
,
Monsalve-Serrano
,
J.
,
Bernal
,
M. A.
, and
Odillard
,
L.
,
2021
, “
Impacts of the Exhaust Gas Recirculation (EGR) Combined With the Regeneration Mode in a Compression Ignition Diesel Engine Operating at Cold Conditions
,”
Int. J. Engine Res.
,
22
(
12
), pp.
3548
3557
.
41.
Al-lwayzy
,
S. H.
,
Yusaf
,
T.
,
Saleh
,
K.
, and
Yousif
,
B.
,
2019
, “
The Influence of Emulsified Water Fuel Containing Fresh Water Microalgae on Diesel Engine Performance, Combustion, Vibration and Emission
,”
Energies
,
12
(
13
), p.
2546
.
42.
Hu
,
Y.
,
Huang
,
Z.
,
Wang
,
L.
,
Sun
,
X.
, and
Chen
,
W.
,
2022
, “
Experimental Study on Combustion and Emissions of a Compression Ignition Engine Fueled With Gasoline
,”
Adv. Mech. Eng.
,
14
(
7
), p.
168781322211099
.
43.
Bhuiya
,
M.
,
Rasul
,
M.
,
Khan
,
M.
, and
Ashwath
,
N.
,
2019
, “
Performance and Emission Characteristics of a Compression Ignition (CI) Engine Operated With Beauty Leaf Biodiesel
,”
Energy Procedia
,
160
, pp.
641
647
.
44.
Zhang
,
J.
,
Yu
,
X.
,
Guo
,
Z.
,
Li
,
Y.
,
Zhang
,
J.
, and
Liu
,
D.
,
2022
, “
Study on Combustion and Emissions of a Spark Ignition Engine With Gasoline Port Injection Plus Acetone–Butanol–Ethanol (ABE) Direct Injection Under Different Speeds and Loads
,”
Energies
,
15
(
19
), p.
7028
.
45.
Northrop
,
W. F.
,
Fang
,
W.
, and
Huang
,
B.
,
2013
, “
Combustion Phasing Effect on Cycle Efficiency of a Diesel Engine Using Advanced Gasoline Fumigation
,”
ASME J. Eng. Gas Turbines Power
,
135
(
3
), p.
032801
.
46.
Dec
,
J. E.
,
2009
, “
Advanced Compression-Ignition Engines—Understanding the In-Cylinder Processes
,”
Proc. Combust. Inst.
,
32
(
2
), pp.
2727
2742
.
47.
Heywood
,
B.
,
2011
,
Internal Combustion Engine Fundamentals
,
Tata McGraw-Hill
,
New Delhi
.
48.
Kamimoto
,
T.
, and
Bae
,
M.
,
1988
, “High Combustion Temperature for the Reduction of Particulate in Diesel Engines,” SAE Technical Paper.
49.
Shuai
,
S.
,
Wang
,
B.
,
Yang
,
H.
,
Wang
,
Z.
,
Wang
,
J.
,
He
,
X.
, and
Xu
,
H.
,
2014
, “
Combustion and Emission Characteristics of Multiple Premixed Compression Ignition (MPCI) Mode With Low Octane Gasoline Fuels
,”
Energy Procedia
,
61
, pp.
2127
2131
.
50.
Curran
,
S.
,
Szybist
,
J.
,
Kaul
,
B.
,
Easter
,
J.
, and
Sluder
,
S.
,
2021
, “
Fuel Stratification Effects on Gasoline Compression Ignition With a Regular-Grade Gasoline on a Single-Cylinder Medium-Duty Diesel Engine at Low Load
,”
SAE Tech. Paper
,
4
(
2
), pp.
488
501
.
51.
Sellnau
,
M.
,
Sinnamon
,
J.
,
Hoyer
,
K.
, and
Husted
,
H.
,
2011
, “
Gasoline Direct Injection Compression Ignition (GDCI)—Diesel-Like Efficiency With Low CO2 Emissions
,”
SAE Int. J. Engines
,
4
(
1
), pp.
2010
2022
.
52.
Syafiq
,
Z.
,
Fahmi
,
O.
,
Syuhaida
,
N.
,
Chen
,
A. F.
, and
Adam
,
A.
,
2017
, “
Diesel Engine Performance and Exhaust Emission Analysis Using Diesel-Organic Germanium Fuel Blend
,”
MATEC Web Conf.
,
90
, p.
01053
.
53.
Jalaludin
,
H. A.
,
Abdullah
,
N. R.
,
Sharudin
,
H.
,
Asiah
,
A. R.
, and
Jumali
,
M. F.
,
2020
, “
Emission Characteristics of Biodiesel Ratios of 10%, 20%, and 30% in a Single-Cylinder Diesel Engine
,”
IOP Conf. Ser.: Mater. Sci. Eng.
,
834
(
1
), p.
012066
.
54.
Durbin
,
T. D.
,
Miller
,
J. W.
,
Younglove
,
T.
,
Huai
,
T.
, and
Cocker
,
K.
,
2007
, “
Effects of Fuel Ethanol Content and Volatility on Regulated and Unregulated Exhaust Emissions for the Latest Technology Gasoline Vehicles
,”
Environ. Sci. Technol.
,
41
(
11
), pp.
4059
4064
.
55.
Jabłońska
,
M.
, and
Palkovits
,
R.
,
2016
, “
It Is No Laughing Matter: Nitrous Oxide Formation in Diesel Engines and Advances in Its Abatement Over Rhodium-Based Catalysts
,”
Catal. Sci. Technol.
,
6
(
21
), pp.
7671
7687
.
56.
Ruutelmann
,
M.
,
1993
,
The Importance of HNCO as a Precursor of N2O Formation in Combustion
,” Master's Thesis, Chalmers University of Technology and University of Gotenborg, Sweden.
57.
Rößler
,
M.
,
Koch
,
T.
,
Janzer
,
C.
, and
Olzmann
,
M.
,
2017
, “
Mechanisms of the NO2 Formation in Diesel Engines
,”
MTZ Worldw.
,
78
(
7–8
), pp.
70
75
.
58.
Lin
,
C.
,
Jeng
,
Y.
,
Wi
,
C.
, and
Wu
,
K.
,
1996
, “
Influences of Fuel Sulfur Content on Diesel Engine Emission Characteristics Under Varying Temperature and Humidity of Inlet Air
,”
J. Environ. Sci. Health Part A Environ. Sci. Eng. Toxicol.
,
31
(
4
), pp.
765
782
.
59.
Obeid
,
F.
,
Van
,
T. C.
,
Horchler
,
E. J.
,
Guo
,
Y.
,
Verma
,
P.
,
Miljevic
,
B.
,
Brown
,
R. J.
,
Ristovski
,
Z.
,
Bodisco
,
T.
, and
Rainey
,
T.
,
2022
, “
Engine Performance and Emissions From Fuels Containing Nitrogen and Sulphur
,”
Energy Convers. Manage. X
,
14
, p.
100179
.
60.
Fleig
,
D.
,
Andersson
,
K.
, and
Johnsson
,
F.
,
2012
, “
Influence of Operating Conditions on SO3 Formation During Air and Oxy-Fuel Combustion
,”
Ind. Eng. Chem. Res.
,
51
(
28
), pp.
9483
9491
.
61.
Mitchell
,
C. E.
, and
Olsen
,
D. B.
,
2000
, “
Formaldehyde Formation in Large Bore Natural Gas Engines Part 1: Formation Mechanisms
,”
ASME J. Eng. Gas Turbines Power
,
122
(
4
), pp.
603
610
.
62.
Yu-sheng
,
Z.
,
Chun-lan
,
M.
,
Hai-ying
,
S.
, and
Shao-ren
,
Z.
,
2007
, “Study on Formaldehyde Emission in a DME-Fueled Direct-Injection Diesel Engine,” SAE Technical Papers.
63.
Alzueta
,
M. U.
, and
Glarborg
,
P.
,
2003
, “
Formation and Destruction of CH2O in the Exhaust System of a Gas Engine
,”
Environ. Sci. Technol.
,
37
(
19
), pp.
4512
4516
.
64.
Musculus
,
M. P. B.
,
Miles
,
P. C.
, and
Pickett
,
L. M.
,
2013
, “
Conceptual Models for Partially Premixed Low-Temperature Diesel Combustion
,”
Prog. Energy Combust. Sci.
,
39
(
2–3
), pp.
246
283
.
65.
Suarez-Bertoa
,
R.
, and
Astorga
,
C.
,
2016
, “
Isocyanic Acid and Ammonia in Vehicle Emissions
,”
Transp. Res. D: Transp. Environ.
,
49
, pp.
259
270
.
66.
Jathar
,
S. H.
,
Heppding
,
C.
,
Link
,
M. F.
,
Farmer
,
D. K.
,
Akherati
,
A.
,
Kleeman
,
M. J.
,
de Gouw
,
J. A.
,
Veres
,
P. R.
, and
Roberts
,
J. M.
,
2017
, “
Investigating Diesel Engines as an Atmospheric Source of Isocyanic Acid in Urban Areas
,”
Atmos. Chem. Phys.
,
17
(
14
), pp.
8959
8970
.
67.
Hansson
,
K.-M.
,
Samuelsson
,
J.
,
Tullin
,
C.
, and
Åmand
,
L.-E.
,
2004
, “
Formation of HNCO, HCN, and NH3 From the Pyrolysis of Bark and Nitrogen-Containing Model Compounds
,”
Combust. Flame
,
137
(
3
), pp.
265
277
.
68.
Nie
,
B.
,
Peng
,
C.
,
Wang
,
K.
, and
Yang
,
L.
,
2020
, “
Structure and Formation Mechanism of Methane Explosion Soot
,”
ACS Omega
,
5
(
49
), pp.
31716
31723
.
69.
Espinal
,
J. F.
,
Mondragón
,
F.
, and
Truong
,
T. N.
,
2005
, “
Mechanisms for Methane and Ethane Formation in the Reaction of Hydrogen With Carbonaceous Materials
,”
Carbon
,
43
(
9
), pp.
1820
1827
.
70.
Boot
,
M. D.
,
Tian
,
M.
,
Hensen
,
E. J. M.
, and
Mani Sarathy
,
S.
,
2017
, “
Impact of Fuel Molecular Structure on Auto-Ignition Behaviour—Design Rules for Future High-Performance Gasolines
,”
Prog. Energy Combust. Sci.
,
60
, pp.
1
25
.
71.
Burgoyne
,
J. H.
, and
Hirsch
,
H.
,
1954
, “
The Combustion of Methane at High Temperatures
,”
Proc. R. Soc. A
,
227
, pp.
73
93
.
72.
Birkavs
,
A.
, and
Smigins
,
R.
,
2018
, “
An Assessment of Stratification of Exhaust Gases From Gasoline and Diesel Engine
,”
Agron Res.
,
16
, pp.
977
984
.
73.
Blanquart
,
G.
,
Pepiot-Desjardins
,
P.
, and
Pitsch
,
H.
,
2009
, “
Chemical Mechanism for High-Temperature Combustion of Engine-Relevant Fuels With Emphasis on Soot Precursors
,”
Combust. Flame
,
156
(
3
), pp.
588
607
.
74.
Singh
,
A. P.
, and
Agarwal
,
A. K.
,
2021
, “
Performance and Emission Characteristics of Conventional Diesel Combustion/Partially Premixed Charge Compression Ignition Combustion Mode Switching of Biodiesel-Fueled Engine
,”
Int. J. Engine Res.
,
22
(
2
), pp.
540
553
.
75.
Senneca
,
O.
, and
Tucciullo
,
T.
,
2020
, “
Lumped Kinetics for Homogeneous Reactions of n-Hexadecane and n-Decene as Model Compounds for PE Pyrolysis Primary Tars
,”
Energies
,
13
(
20
), p.
5466
.
76.
Maffina
,
A.
,
Roussillo
,
M.
,
Scouflaire
,
P.
,
Darabiha
,
N.
,
Veynante
,
D.
,
Candel
,
S.
, and
Franzelli
,
B.
,
2024
, “
Role of the Equivalence Ratio on Soot Formation in a Perfectly Premixed Turbulent Swirled Flame: A Combined Experimental and Large Eddy Simulations Study
,”
ASME J. Eng. Gas Turbines Power
,
146
(
6
), p.
061012
.
77.
Liang
,
X.
,
Zhu
,
Z.
,
Cao
,
X.
,
Wang
,
K.
, and
Wang
,
Y.
,
2022
, “
Research on the Soot Generation of Diesel Surrogate Mechanisms of Different Carbon Chain Lengths
,”
Energies
,
15
(
20
), p.
7625
.
78.
Zhang
,
M.
,
Ong
,
J. C.
,
Pang
,
K. M.
,
Bai
,
X.-S.
, and
Walther
,
J. H.
,
2022
, “
Effects of Ambient CO2 and H2O on Soot Processes in n-Dodecane Spray Combustion Using Large Eddy Simulation
,”
Fuel
,
312
, p.
122700
.
79.
Cung
,
K. D.
,
Ciatti
,
S. A.
,
Tanov
,
S.
, and
Andersson
,
Ö.
,
2017
, “
Low-Temperature Combustion of High Octane Fuels in a Gasoline Compression Ignition Engine
,”
Front. Mech. Eng.
,
3
(
Article 22
), p. pp.
1
14
.
80.
Zhang
,
Y.
,
Wang
,
Q.
,
Yang
,
R.
,
Yan
,
Y.
,
Fu
,
J.
, and
Liu
,
Z.
,
2022
, “
Numerical Investigation of the Effect of Injection Timing on the In-Cylinder Activity of a Gasoline Direct Injection Engine
,”
Adv. Mech. Eng.
,
14
(
3
), p.
168781322210828
.
81.
Liu
,
H.-J.
,
Chen
,
R.-H.
, and
Wang
,
W.-C.
,
2020
, “
The Non-Regulated Emissions From a Turbo-Charged Diesel Engine Under Steady-State Operation With Hydro-Processed Renewable Diesel (HRD)
,”
Fuel
,
263
, p.
116762
.
82.
Bermúdez
,
V.
,
Lujan
,
J. M.
,
Pla
,
B.
, and
Linares
,
W. G.
,
2011
, “
Comparative Study of Regulated and Unregulated Gaseous Emissions During NEDC in a Light-Duty Diesel Engine Fuelled With Fischer Tropsch and Biodiesel Fuels
,”
Biomass Bioenergy
,
35
(
2
), pp.
789
798
.
83.
Ruan
,
J.
,
Xiao
,
H.
,
Yang
,
X.
,
Guo
,
F.
,
Huang
,
J.
, and
Ju
,
H.
,
2021
, “
Effects of Injection Timing on Combustion Performance and Emissions in a Diesel Engine Burning Biodiesel Blended With Methanol
,”
Therm. Sci.
,
25
(
4 Part A
), pp.
2819
2829
.
84.
Zhou
,
Y.
,
Wu
,
J.
, and
Lemmon
,
E. W.
,
2012
, “
Thermodynamic Properties of o-Xylene, m-Xylene, p-Xylene, and Ethylbenzene
,”
J. Phys. Chem. Ref. Data
,
41
(
2
), p.
023103
.
85.
Mirkin
,
D. B.
,
2007
, “Benzene and Related Aromatic Hydrocarbons,”
Haddad and Winchester’s Clinical Management of Poisoning and Drug Overdose
,
Elsevier
, pp.
1363
1376
.
86.
Daniel
,
R. L.
,
2012
, “
Combustion and Emissions Performance of Oxygenated Fuels in a Modern Spark Ignition Engine
,” Thesis, The University of Birmingham, UK.
87.
Platt
,
S. M.
,
El Haddad
,
I.
,
Pieber
,
S. M.
,
Zardini
,
A. A.
,
Suarez-Bertoa
,
R.
,
Clairotte
,
M.
,
Daellenbach
,
K. R.
, et al
,
2017
, “
Gasoline Cars Produce More Carbonaceous Particulate Matter Than Modern Filter-Equipped Diesel Cars
,”
Sci. Rep.
,
7
(
1
), p.
4926
.
88.
Puškár
,
M.
,
Živčák
,
J.
,
Král
,
Š.
,
Kopas
,
M.
, and
Lavčák
,
M.
,
2021
, “
Analysis of Biodiesel Influence on Unregulated Gaseous Emissions of Diesel Motor Vehicles
,”
Appl. Sci.
,
11
(
10
), p.
4646
.
89.
Hellier
,
P.
,
Ladommatos
,
N.
,
Allan
,
R.
, and
Rogerson
,
J.
,
2013
, “
Combustion and Emissions Characteristics of Toluene/n-Heptane and 1-Octene/n-Octane Binary Mixtures in a Direct Injection Compression Ignition Engine
,”
Combust. Flame
,
160
(
10
), pp.
2141
2158
.
90.
Ji
,
C.
,
Sarathy
,
S. M.
,
Veloo
,
P. S.
,
Westbrook
,
C. K.
, and
Egolfopoulos
,
F. N.
,
2012
, “
Effects of Fuel Branching on the Propagation of Octane Isomers Flames
,”
Combust. Flame
,
159
(
4
), pp.
1426
1436
.
91.
Agarwal
,
A. K.
,
Prashumn, Valera
,
H.
, and
Nath Mustafi
,
N.
,
2022
, “
Di-Ethyl Ether-Diesel Blends Fuelled Off-Road Tractor Engine: Part-II: Unregulated and Particulate Emission Characteristics
,”
Fuel
,
308
, p.
121973
.
92.
Sarıkoç
,
S.
,
2020
, “Fuels of the Diesel-Gasoline Engines and Their Properties,”
Diesel and Gasoline Engines
,
IntechOpen
, London.