Triple Injection Strategies Research Articles

Ammonia combustion using hydrogen jet ignition (AHJI) in internal combustion engines

The application of ammonia and hydrogen in internal combustion engines (ICE) is a promising zero-carbon technology. This paper investigates ammonia combustion in ICE using hydrogen multiple-injection jet-ignition (MIJI). The experiment was conducted on a single-cylinder heavy-duty engine with a compression ratio of 17 and a cylinder bore of 123 mm. In the passive jet ignition mode, the minimum hydrogen energy ratio for stable operation of the ammonia-hydrogen engine was 15 %. Using H2 active jet ignition could improve the combustion stability significantly. It was found that engine performance was gradually improved by H2 injection strategy in order of single-injection, double-injection to triple-injection. The triple-injection strategy could achieve a more ideal distribution of ammonia-hydrogen mixture: the first injection forms a homogeneous mixture to increase fuel reactivity; the second injection creates a stratified hydrogen mixture, facilitating rapid flame propagation; the third injection forms a relatively rich mixture in the jet chamber conducive to spark ignition. Through the optimization of the hydrogen injection strategy and spark timing, stable combustion (COV = 1 %) and high thermal efficiency (ITE = 42.5 %) in ammonia-hydrogen engines were achieved, with a minimum hydrogen energy ratio less than 3 %.

Effect of wall-impingement distance on fuel adhesion characteristics of split injection spray under cross-flow condition

In direct-injection spark ignition (DISI) engines, high-pressure fuel injectors introduce fuel into the cylinder, causing the spray to come into contact with and adhere to the cylinder wall; this is known as fuel adhesion. Over time, fuel adhesion contributes to carbon deposition on the cylinder wall, which affects its thermal conductivity and consequently diminishes engine combustion efficiency. This study investigates the influence of different impingement distances and cross-flow velocities on fuel adhesion under the triple injection strategy. The fuel adhesion propagation and side-view spray are measured using refractive index matching (RIM) and Mie scattering, respectively. The findings demonstrate that high cross-flow velocity promotes the fuel adhesion shape to be elongated strips. In the early stage, the growth rate of the fuel adhesion area increases with an increase in cross-flow velocity. In the later stage, the decrease rate in the fuel adhesion area initially increases with an increase in the cross-flow velocity; however, when the critical velocity threshold (20 m/s) is exceeded, the decrease rate in the fuel adhesion area tends to stabilize. The average fuel adhesion thickness then accordingly decreases with the increase in the cross-flow velocity and impingement distance in the later stage. In addition, the cross-flow promotes the volatilization of spray and fuel adhesion, thereby decreasing the fuel adhesion mass over time. In the context of carbon neutrality, this study underscores the importance of optimizing fuel injection conditions to reduce emissions and fuel consumption.

Effect of Fuel Injection Strategies on Performance, Regulated and Unregulated Emissions of a Gasoline Compression Ignition Engine

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.

Improving the lean burn performance of a high compression ratio methanol engine by multiple-injection

Methanol is a promising fuel for achieving carbon neutrality in sectors requiring internal combustion engines. The multiple-injection approach is effective in reducing cycle-to-cycle variations and improving the performance of methanol engines under lean burn conditions. This study proposes a concept for transforming diesel engines into methanol engines with flexible injection and lean burning capabilities. This study fills the research gap in the study of lean methanol combustion in swirl combustion chambers. The effects of 22 different multiple-injection strategies on combustion characteristics, emission performance, and combustion stability are experimentally assessed in a direct-injection spark ignition engine with an excess air ratio (λ) of 1.35. Each multiple-injection strategy is comprehensively evaluated using a merit function and compared with the baseline case that uses single injection. The results show that the double- and triple-injection strategies substantially shorten the durations of combustion and flame development. Therefore, a higher effective expansion ratio is obtained. Meanwhile, the cycle-to-cycle variation in the IMEP decreases from 4.2% of the baseline to 1.49% at T8. CO and HC emissions deteriorate; however, NOx and CO2 emissions under triple injection are lower than those under the baseline. The T7 case with triple injection achieves the highest thermal efficiency, which is 6.8% higher than that for the baseline case. Overall, triple injection achieves higher merit function values, which indicates a better capability to improve lean-burn performance than double injection.

Experimental Evaluation of Pilot and Main Injection Strategies on Gasoline Compression Ignition Engine—Part 2: Performance and Emissions Characteristics

<div>Internal combustion (IC) engines play an important role in the global economy by powering various transport applications. However, it is a leading cause of urban air pollution; therefore, new combustion strategies are being developed to control emissions. One promising advanced low-temperature combustion (LTC) technology is gasoline compression ignition (GCI). This experimental study assesses the performance of a two-cylinder engine, emissions, and exhaust particulate characteristics using G80 (80% v/v gasoline and 20% v/v diesel) blend operating in GCI mode vis-à-vis baseline conventional diesel combustion (CDC) mode using diesel. The effects of double pilot injection, Pilot-1 proportion (10–30%), and main injection timing were investigated on the GCI combustion. Experiments were performed at different engine loads (3, 4, and 5 bar brake mean effective pressure [BMEP]) at a constant engine speed (2000 rpm). GCI combustion showed higher brake thermal efficiency (BTE) than CDC mode at medium loads. Hydrocarbon (HC) and carbon monoxide (CO) emissions increased in GCI mode, but oxides of nitrogen (NOx) were reduced than the baseline CDC mode. High pilot ratio and late main injection timing tests showed higher HC and CO emissions in the GCI mode at low engine loads. The GCI mode engine emitted higher nucleation mode particles and nanoparticles than baseline CDC mode at high engine loads. Using a triple injection strategy, GCI engines simultaneously reduced NOx and particulate matter (PM) emissions, especially at high loads. Controlling these emissions in baseline CDC mode engines is otherwise quite challenging.</div>

An Experimental and Computational Study on Triple Injection Strategies to Reduce Cold Start Diesel Engine Emissions

Abstract The effect of triple injection strategies in a diesel engine to reduce cold start emissions were experimentally and computationally investigated in this work. The experiments were performed using a 1.9 L four-cylinder, turbocharged compression ignition engine with diesel fuel. As a representative of the cold start condition in the diesel engine, a low load condition of 1500 rpm and 2 bar brake mean effective pressure (BMEP) was chosen as the fixed condition for this study. The injection strategy made use of a late post injection to reduce catalyst light-off time. The pilot and main injections are fixed and the post injection timing is swept later into the expansion stroke to increase exhaust enthalpy available to heat the aftertreatment system. To further understand the source of hydrocarbon (HC) emissions from late injections, equivalent experiments were conducted with a mixture of n-heptane and iso-octane that matched the reactivity of the diesel fuel. The mixture of primary reference fuels (i.e., PRF 34) obtained by matching the cetane number (CN) of diesel fuel, showed similar combustion characteristics of diesel, but is much more volatile due to lighter components in the PRF mixture. The increased volatility of PRF 34 suppressed liquid fuel impingement on the cylinder liner, which isolated liner impingement as a possible source of HC emissions. Simulations were also performed for the present engine configuration and operating conditions in a sector mesh using CONVERGE™. The physical properties of diesel fuel were modeled using a five-component surrogate. The chemical kinetics of the diesel fuel were modeled with a reduced n-heptane model. The simulations were able to capture the experimental trends of combustion characteristics and emissions. The HC emissions were observed to increase for both fuels with retarded post injection timings in engine experiments. PRF 34 had comparable HC emissions to diesel experiments, which indicated that the liner impingement is not the main source of the increase in HC emissions. Overmixing of the fuel and air was identified as the major cause of increase in HC emissions. Additionally, exhaust gas recirculation (EGR) also intensified the overmixing phenomenon and thereby increase in HC emissions.

ASSESSMENT OF THE QUADRUPLE INJECTION STRATEGY OVER TRIPLE INJECTIONS TO IMPROVE EMISSIONS, PERFORMANCE AND NOISE OF THE AUTOMOTIVE DIESEL ENGINE

The present study aims at investigating effectiveness of the quadruple (early-pilot-main-after [epMa]) injection strategy over three different triple [early-main-after (eMa), early-pilot-main (epM) and pilot-main-after (pMa)] injection scheduling in terms of emissions, performance [brake specific fuel consumption (BSFC), torque, brake thermal efficiency (BTE) and fuel economy] and noise. The experimentation was carried out on a heavy-duty BS-IV diesel engine with 45% EGR fraction and fixed main injection (Crank-angle) scheduling at eight different RPMs and three loads of engine (20%, 60% and 100%) using design of experiments(DOE). This comprehensive study showed that the quadruple injection strategy provides optimum results in both performance and emissions compared to the promising three triple injection strategy. The quadruple injection strategy exhibits the best BTE at all operating conditions and best BSFC at medium to high-speed zone around 0.5–1% inline to reduce combustion noise (CN) level, especially at low speeds and low to medium load of 0.2–2.2 dBA. Among triple injections, the pMa shows the best performance in BSFC, BTE, smoke and THC emissions. The epM is the best in the CO emissions and torque performance in the low-speed zone. Smoke value is marginally higher for the epMa at low to medium speed than the pMa, although average smoke emissions were the best. Taken together, the overall PM emission level was marginally better than Triple Injections, due to the impact of double pilots in combination with post-injection. In addition, NOx emissions were improved (around 3–6%) significantly with quadruple than with triple injections. The epMa injection scheduling also showed improvement in constant speed fuel economy and in pass-by-noise at the vehicle.

Application of methanol and optimization of mixture design over the full operating map in an intelligent charge compression ignition (ICCI) engine

Application of methanol and mixture design of the dual-fuel intelligent charge compression ignition (ICCI) was investigated over the full operating range. ICCI engine (an originally 5.3 L turbocharged diesel engine) equipped with two direct-injection systems and a supercharged system realized real-time design of dual-fuel stratification and was investigated compared with conventional diesel combustion (CDC). Engine operating map and control strategy was obtained, and combustion characteristics and original emissions were analyzed. Results showed that the thermal efficiency of ICCI was 1% to 3% higher than that of CDC in the load range of 6–14 bar IMEP. Increasing load over 14 bar IMEP, a triple-injection strategy of methanol was applied where the last injection was near the top dead center. Except for high speed and low load conditions, ICCI mode realized controllable combustion (coefficient of cyclic variation below 5%, maximum pressure rise rate below 15 bar/°CA, and peak pressure below 180 bar). The maximum thermal efficiency was 53% under low speed and high load conditions, while the minimum NOx emissions were 0.17 g/kWh occurring in the same conditions. Nucleation particles dominated the formation of particle emissions and were minimized under high speed and medium load conditions (below 1.3 × 106/cm3).

High Load Compression Ignition of Wet Ethanol Using a Triple Injection Strategy

Wet ethanol is a biofuel that can be rapidly integrated into the existing transportation sector infrastructure and have an immediate impact on decarbonization. Compared to conventional hydrocarbon fuels, wet ethanol has unique fuel properties (e.g., short carbon chain, oxygenated, high heat of vaporization, no cool-flame reactivity), which can actually improve the efficiency and engine-out emissions of internal combustion engines while decarbonizing. In this work, wet ethanol 80 (80% ethanol, 20% water by mass) was experimentally studied at high loads under boosted conditions in compression ignition to study the tradeoffs in efficiency and emissions based on boosting and injection strategies. Specifically, this work explores the potential of adding a third, mixing-controlled injection at high loads. The results indicate that adding a third, mixing-controlled injection results in combustion stabilization at high loads, where the peak pressure limit of the engine is a constraint that requires combustion phasing to retard. However, since the heat of vaporization of wet ethanol 80 is ~6% of its lower heating value, evaporation of fuel injected near top dead center imposes a thermodynamic efficiency penalty by absorbing heat from the working fluid at a time in the cycle when adding heat produces net work out. Additionally, the mixing-controlled injection increases NOx emissions. Therefore, the amount of fuel injected in the mixing-controlled injection should be limited to only what is necessary to stabilize combustion. Ultimately, by using wet ethanol 80 in a triple injection strategy, a load of 22 bar IMEPn is achieved with a net fuel conversion efficiency of 42.2%, an engine-out indicated specific emissions of NOx of 1.3 g/kWh, and no measurable particulate matter, while maintaining a peak cylinder pressure below 150 bar.

Comparative analysis on single, double and triple fuel injection strategy of single cylinder RCCI engine fueled with ethanol-gasoline/diesel-biodiesel blends

This experimentation attempts to investigate the parametric and comparative analysis of single, double and triple injection strategies of DI (direct injection) for modified constant speed non road single cylinder RCCI engine. The blends of ethanol-gasoline and diesel- jatropha biodiesel were used as a low reactivity fuel (LRF) and high reactivity fuel (HRF), respectively. The ratio of LRF and HRF was 60:40. The following parameters were employed in this experiment: 12% hot exhaust gas recirculation (EGR), 3 bar PFI (port fuel injection) pressure, and 500 bar HRF injection. In the case of single injection strategy, injection timing was −25 deg atdc with 100% mass, for double injection strategy −40 deg and-18 deg atdc with 40% and 60% mass and triple injection, −31 deg, −21 deg and −11 deg atdc with 30%,30% and 40% masses respectively. All the tests were performed at 1500 rpm speed and under various loading conditions ranging from 0 to 12 kg in increments of 4 kg. Results were compared with a double injection strategy for 12 kg loading conditions. It has been observed that for single injection 6% reduction in HC emission,67.5%,25% and 2% rise in NOx, CO and smoke opacity respectively, while for triple injection strategy, 25 % and 41.78% rise in HC and NOx emission and 8% and 15.78% reduction in CO and smoke opacity respectively . From the results it has been concluded that proper tuned multiple injections of the biofuelled RCCI operation have great potential to reduce the emission constituents without affecting the performance of the engine.

Effect of Conical Spray and Multi-Hole Spray on Gasoline Engine Mixture Formation and Combustion Performance Based on Different Injection Strategies

Abstract This article presents a numerical investigation carried out to determine the effects of second and third injection timing on combustion characteristics and mixture formation of a gasoline direct injection (GDI) engine by comparing conical spray against multihole spray. The results showed that at the engine 80% full load of 2000 r/min, the difference in mixture distribution between the two sprays was obvious with double and triple injection strategies. With the second injection timing from 140 deg CA delay to 170 deg CA, the in-cylinder pressure, the in-cylinder temperature, and the heat release rate of the conical spray increased by 20.8%, 9.8%, and 30.7% and that of the multihole spray decreased by 30.7%, 13.6%, and 37.8%. The delay of the injection time reduced the performance of the engine with the multihole spray, and the performance of the multihole spray was obviously in the simulation of the triple injection strategy. However, for the conical spray, the application of the triple injection strategy increased the temperature and the pressure compared with the double injection strategy.

The Role of Multiple Injections on Combustion in a Light-Duty PPC Engine

This paper presents a numerical investigation of the ignition and combustion process of a primary reference fuel in a partially premixed light-duty internal combustion (PPC) engine. Partially pre-mixed combustion is achieved by employing a multiple injection strategy with three short injection events of fuel pulses. The timing of the first two fuel pulses, 48 and 22 crank angle degrees before top dead center, are chosen with the purpose to stratify the fuel and air charge, whereas the third injection, at five crank angle degrees before top dead center, serves as an actuator of the main heat release. In addition to this baseline injection, three alternative injection strategies are studied, including a split-fuel two-injection strategy and modified triple-injection strategies. Large eddy simulations are employed utilizing a skeletal chemical kinetic mechanism for primary reference fuel capable of capturing the low-temperature ignition and the high temperature combustion. The large eddy simulation (LES) results are compared with experiments in an optical accessible engine. The results indicate that the first ignition sites are in the bowl region where the temperature is relatively higher, and the reaction fronts thereafter propagate in the swirl direction and towards the centerline of the cylinder. The charge from the first two injections initially undergoes low-temperature reactions and thereafter high-temperature reservoirs are formed in the bowl region. The main heat-release is initiated in the engine when the fuel from the third injection reaches the high-temperature reservoirs. Finally, the remaining fuel in the lean mixtures from the first two injections is oxidized. By variation of the injection strategy, two trends are identified: (1) by removing the second injection a higher intake temperature is required to enable the ignition of the charge, and (2) by retarding second injection, a longer ignition delay is identified. Both can be explained by the stratification of fuel and air mixture, and the resulting reactivity in various equivalence ratio and temperature ranges. The LES results reveal the details of the charge stratification and the subsequent heat release process. The present results indicate a rather high sensitivity of partially premixed combustion process to the injection strategies.

Effects of different injection strategies on ignition and combustion characteristics in an optical PPC engine

abstract Although multiple injection strategies have a significant influence on partially premixed combustion (PPC) efficiency, the mechanisms behind the influence are still to be explained and evaluated. In this paper, single, double, and triple injection strategies are used in a heavy-duty optical engine. The effects on engine efficiency are analyzed by an energy balance method. Furthermore, the change of ignition location and combustion process under different injection cases are explored by natural luminescence recorded by a high-speed camera. The results show that, with double injections, the interaction between the main and pilot jets advances the combustion phasing nearly to the top dead center (TDC), resulting in higher efficiency. This interaction also shifts the combustion process into the piston bowl, where it has high potential to reduce heat-transfer loss. With triple injections, the interaction between the main combustion (formed by the pilot and main injections) and the post injection jet significantly affects the combustion losses. In all, the jet-jet interaction and combustion-jet interactions play a significant role in engine efficiency when using multiple injections.

Effects of Rate-Shaped and Multiple Injection Strategies on Pollutant Emissions, Combustion Noise and Fuel Consumption in a Low Compression Ratio Diesel Engine

An experimental investigation has been carried out to highlight the effects of different injection strategies on the performance and emissions of a low compression ratio Euro 5 diesel engine operated with high EGR rates. Rate-shaped main injections, achieved with piezoelectric and solenoid injectors by means of boot and injection fusion, respectively, as well as optimized multiple injection patterns have been compared. The results of the comparisons, performed with reference to a state-of-the-art double pilot-Main (pM) strategy, are presented in terms of engine-out exhaust emissions, combustion noise (CN) and fuel consumption. Rate-shaped main injections, when included in delayed multiple injection patterns, have shown a minor influence on reducing NOx, while a slight deterioration in soot has been found. Both a double pilot and a boot injection schedule have been able to reduce CN at low loads. A higher reduction in CN has been obtained with an injection fusion event. Finally, DoE optimized triple and quadruple injection strategies have led to improved soot-NOx trade-offs, with respect to the pM calibration. In fact, splitting the injection helps to entrain air inside the fuel plumes, thus creating locally leaner mixture (less prone to forming soot) and allowing increasing the EGR rates (reducing NOx formation).

Manipulating heat release features to minimize combustion noise

Changes in combustion noise, efficiency, and emissions are investigated as responses to boundary conditions and injection scheduling parameters of closely-coupled multiple-pilot strategies. In order to minimize combustion noise, the heat release rate (HRR) should be as linear in its buildup as possible. Through low injection pressure, high dilution ratio, and close-coupling of the pilot injections, combustion noise can be minimized. It is possible to have too much mixture dilution or dwells which are too short, however. This causes excessive blending of combustion events which tends to increase combustion noise. High injection pressure can significantly decrease soot emissions without significantly increasing combustion noise. This is beneficial since high dilution ratios will increase soot emissions but are desirable to achieve both lower NOx and combustion noise levels. Noise minimization though HRR shaping has also been achieved through injection rate shaping. Based on the learnings from each investigation, triple and quadruple-pilot injection strategies are created for lowest possible combustion noise. The investigations also reveal the relative extent to which emissions, noise, and efficiency are affected by each control parameter so that compromises in each response can be understood.

A comprehensive analysis of multiple injection strategies for improving diesel combustion process under cold-start conditions

Cold start in diesel engines is an issue of increasing importance due to its high fuel consumption and emissions. In cold-start operations, improving the combustion process is directly related to improving the thermal efficiency and emissions. In this study, a comprehensive analysis of multiple injection strategies was conducted under cold-start conditions to identify an optimal injection strategy that improves diesel combustion process at various ambient temperatures. The cold-start conditions were reproduced in a constant volume combustion chamber (CVCC). While all of the sprays in a single injection strategy were successfully ignited at 293 K, only the sprays near a glow plug showed combustion reactions at 253 K. The low air and diesel temperature at 253 K inhibited the diesel vaporization, which led to the poor combustion development. Pilot injections were implemented to improve the diesel vaporization at 253 K. The pilot injections had a small amount of heat required to vaporize diesel droplets, which reduced the temperature drop in the combustion chamber. The pilot injections also released small amounts of heat prior to the following main injection, thus aiding the vaporization of the main injection. The triple and quadruple injections improved the combustion process significantly at 253 K. However, the double and triple injections showed superior heat release rate and in-chamber pressure rise at 293 K. Based on the results at 253 K and 293 K, the triple injection strategy were determined to be the optimal injection strategy under cold-start conditions.

Combustion stability study of partially premixed combustion by high-pressure multiple injections with low-octane fuel

This work is the second part of a study on low-load combustion stability for gasoline partially premixed combustion. In part 1, we investigated the sensitivity of the intake air temperature to combustion stability. In part 2, we evaluate the potential of the multiple-injection strategy along with the intake air temperature sensitivity to promote low-load combustion stability using low-octane gasoline fuel. The experiments were carried out in a fully transparent, single-cylinder, compression-ignition engine. The spray/wall interaction, particularly the fuel trapping in the piston crevice zone, was visualized by fuel-tracer planar laser-induced fluorescence for the first time in experiments. The in-cylinder combustion process of natural flame luminosity was captured by a high-speed color camera. By employing a multiple-injection strategy, the minimum intake air temperature can be further reduced from 70 °C (single injection) to 50 °C for target stable combustion. The combustion stability and engine performance were further improved by increasing the fuel injection pressure. For instance, with the triple-injection strategy at a higher fuel-injection pressure of 800 bar, the indicated mean effective pressure was increased by 24% when compared to that of the single-injection strategy. A stronger interaction among fuel spray jets, the piston, and the cylinder wall was observed for multiple injections with higher injection pressure, leading to higher unburned hydrocarbon (UHC) and carbon monoxide (CO) along with a more pronounced pool fire in the squish zone. The double-injection strategy resulted in lower UHC and CO emissions when compared to the triple-injection strategy. Applying a narrow spray angle injector with re-entrant combustion chamber is suggested for optimizing the spray/wall interaction.

Flame Front and Burned Gas Characteristics for Different Split Injection Ratios and Phasing in an Optical GDI Engine

Direct-injection in spark-ignition engines has long been recognized as a valid option for improving fuel economy, reducing CO2 emissions and avoiding knock occurrence due to higher flexibility in control strategies. However, problems associated with mixture formation are responsible for soot emissions, one of the most limiting factors of this technology. Therefore, the combustion process and soot formation were investigated with different injection strategies on a gasoline direct injection (GDI) engine. The experimental analysis was realized on an optically accessible single cylinder engine when applying single, double and triple injection strategies. Moreover, the effect of fuel delivery phasing was also scrutinized by changing the start of the injection during late intake- and early compression-strokes. The duration of injection was split in different percentages between two or three pulses, so as to obtain close to stoichiometric operation in all conditions. The engine was operated at fixed rotational speed and spark timing, with wide-open throttle. Optical diagnostics based on cycle resolved digital imaging was applied during the early and late stages of the combustion process. Detailed information on the flame front morphology and soot formation were obtained. The optical data were correlated to in-cylinder pressure traces and exhaust gas emission measurements. The results suggest that the split injection of the fuel has advantages in terms of reduction of soot formation and NOx emissions and a similar combustion performance with respect to the single injection timing. Moreover, an early injection resulted in higher rates of heat release and in-cylinder pressure, together with a reduction of soot formation and flame distortion. The double injection strategy with higher percentage of fuel injected in the first pulse and early second injection pulse showed the best results in terms of combustion evolution and pollutant emissions. For the operative condition studied, a higher time for mixture homogenization and split of fuel injected in the intake stroke shows the best results.

Improvement of high load performance in gasoline compression ignition engine with PODE and multiple-injection strategy

The effects of PODE and multiple fuel injection strategy on combustion and emission characteristics of a multiple-cylinder gasoline compression ignition (GCI) engine are investigated at high load (BMEP = 16 bar) operation condition with a fixed engine speed of 1660 r/min. Experimental results indicate that the sensitivity of soot emission to the variation of injection parameters is decreased by blending PODE with gasoline, mainly due to the enhanced soot oxidation through PODE’s high oxygen content. The main heat release of gasoline is more strongly affected by its pilot heat release compared to that of gasoline/PODE blends. Low PRRmax (maximum pressure rise rate) of about 4.5 bar/°CA can be obtained for gasoline with multiple-injection strategy, under which condition the advantage of gasoline/PODE blends only embodies in reducing soot emission, which is different from that with single injection strategy. The PHRRMI,max (maximum premixed heat release rate of main injection) and Kmain (heat release acceleration ratio of main injection) of gasoline show more sensitivity to the variation of EGR compared to that of PODE20 with pilot-main injection strategy, and the PHRRMI,max and PRRmax of gasoline increase more rapidly in contrast to that of gasoline/PODE blends as injection pressure increases. At higher injection pressure, the soot of all the fuels can be significantly decreased with penalty in PRRmax, especially for gasoline. It is seen that when PODE20 with triple-injection strategy, 1400 bar injection pressure and 30% EGR were employed under the operation condition with the engine speed of 1660 r/min and BMEP of 16 bar, the NOx of 1.3 g/kWh, soot of 0.007 g/kWh and BSFC of 199.67 g/kWh can be obtained while maintaining PRRmax of about 4.5 bar/°CA.

Effects of Triple Injection Strategies on Performance and Pollutant Emissions of a DI Diesel Engine Using CFD Simulation

One of the main controlling parameters in diesel engine combustion is the fuel – air mixing process that has direct effects on engine performance and pollutant emissions, reviewing over previous literature showed that split injection strategies could satisfy this purpose very well. For the first time and in this paper, pilot and double injection strategies were combined and formed new triple injection strategy that has not been considered by any other researchers. In this study after achieving successful validation between modeling and experimental results for both single and double injection strategies, optimization of triple injection strategy was conducted, in which first pulse of double injection strategy divided in to two pulses, then amount of injected fuel in each pulse kept constant and different delay times between first and second pulse of injections were investigated. For better understanding the processes the injections were done inside the engine, diagrams of heat release rate, in cylinder temperature, in cylinder pressure, NOx and soot emissions were presented. Results showed that decreasing the delay time between second and third pulse of injections could decrease the ratio of premixed combustion of third pulse and in optimum cases, reduction in both NOx and soot emissions could be achieved in comparition with single and double injection strategies, without any significant effects on engine performance. Furthermore, triple injection strategy with second pulse of injection that started at 4 crank angle before top dead center was selected to be the optimum case in reduction of both emissions.