Pilot Injection Strategy Research Articles

Experimental study on the effects of pilot injection strategy on combustion and emission characteristics of ammonia/diesel dual fuel engine under low load

With the rise of the concept of carbon neutrality, carbon-free fuel ammonia has attracted widespread attention from internal combustion engine researchers. Ammonia/diesel dual fuel mode can effectively overcome the ignition difficulty of ammonia in the engine and is an effective measure to promote ammonia combustion. Based on a single-cylinder engine, diesel-ignited ammonia combustion experiments were conducted under conditions of 1200 rpm and 30 % load to systematically study the impact of ammonia energy ratio (AER), pilot injection ratio/timing on the combustion and emission characteristics of the ammonia/diesel dual fuel engine. This study finds that the pilot injection improves the upper limit of AER, reduces the cyclic coefficient of variation (COV). The rapid combustion fraction has been defined to understand the dual fuel combustion process. With the AER increases, the rapid combustion fraction of the single injection increases while the trends of the pilot injection strategy are the opposite. Both NOx emissions of the pilot injection strategies decrease while CO emissions increase. The reduction of NOx emissions may be caused by a decline in in-cylinder temperature. At a 35 % AER,Medium-low pilot injection ratios can increase the indicated mean effective pressure (IMEP), which is because as the pilot injection ratio exceeds 35 %, the growth rate in the effective expansion efficiency (EEE) is lower than that of heat transfer loss. When the pilot injection ratio is 35 %, the highest IMEP is achieved, CO and NOx emissions are cut down by 23 % and 20 %, respectively, compared to the single injection.

Effect of ammonia energy ratio and diesel pilot-injection strategy on the performance of ammonia-diesel dual fuel engine

ABSTRACT The combustion strategy under a higher ammonia energy ratio (AER) is expected to improve the combustion performance of ammonia-diesel dual-fuel (ADDF) engines, leading to additional reductions in greenhouse gas (GHG) emissions. In order to meet the engine’s performance requirements while achieving the low carbon emissions, this study utilized CFD numerical simulations to analyze the combustion and emission characteristics for an ADDF engine at AER levels from 0% to 90%. It focused primarily on evaluating the effectiveness of diesel pilot-injection strategy in reducing GHG emissions at AER50%. The obtained results showed that the unburned NH3 and N2O emissions exhibited an upward trend with the increment of AER, leading to a degradation in the indicated thermal efficiency (ITE), while GHG emissions were more significant than in the original diesel-only combustion mode. Based on AER50%, the ITE exhibited a trend of initially rising and then falling with the increment of diesel pilot-injection ratio (DPR) from 0% to 60%, reaching a maximum value of 47.1% at DPR 40%. At this point, the unburned NH3 emission decreased by 42.4% compared to the DPR0%, and no longer declined after the DPR exceeded 40%. Based on AER 50% and DPR 40%, ITE peaked at 48.1% with the optimal timing for diesel pilot-injection, which represented a 1.6% rise in ITE relative to the original diesel-only combustion mode, while GHG emissions decreased by 35%, and NO emissions increased by 25%.

Ammonia fueled engine with diesel pilot ignition: Approach to achieve ultra-high ammonia substitution

Ammonia is a hydrogen-rich zero-carbon fuel, and is one of the most promising approaches to realize energy decarbonization in the fields of industry and transportation. Efficient operation and emissions control have been the primary obstacle to develop engines with high ammonia energy share. In this study, the combustion and emissions of an ammonia-fueled engine with diesel pilot ignition are investigated, and the target is to achieve ultra-high ammonia substitution with acceptable thermal efficiency. The ammonia energy share is first increased from 30% to 90% at an intermediate load, with a split diesel injection triggering ammonia combustion. It found that the increased ammonia energy share reduces the indicated thermal efficiency from 48.3% to 38.9% with high unburned ammonia emissions. The NOx emissions exhibit a turning point with increased ammonia substitution, which indicates that the NOx emissions transition from the thermal-dominated to the fuel-dominated regime. The diesel pilot injection strategy is then optimized, by advancing the main injection timing and changing the pre-injection amount and the interval between two injection events. Optimized diesel injection controls the ignition timing and combustion process, thereby improving thermal efficiency and emissions at high ammonia energy shares. An ultra-high ammonia energy share of 95% could be finally achieved, and the thermal efficiency is 40.2%. It is also noted that as engine load increases, engine thermal efficiency at an ammonia energy share of 80% could be elevated to 44.2%.

Multi-objective optimization of emission parameters of a diesel engine using oxygenated fuel and pilot injection strategy based on RSM-NSGA III

In this work, a diesel engine fueled with PODE3/n-butanol/diesel blends at high altitudes was optimized using the RSM-NSGA III hybrid optimization methodology to achieve a reduction in emissions. The target parameters of the optimization were soot, NOx, and HC emissions, and the decision variables were the mass ratio of pilot injection (MRPI), pilot injection timing (PIT), mass ratio of PODE3 (MRP) and mass ratio of n-butanol (MRB). Firstly, a three-dimensional simulation model of the CI engine was built in CONVERGE, and the model was verified through experiments. Secondly, the effects of the pilot injection strategy, also known as the pre-injection strategy, on the combustion characteristics of the CI engine were analyzed. Then, an experimental design based on Box-Behnken Design (BBD) was conducted and a mathematical model of the target parameters was obtained using RSM. Finally, the mathematical model of RSM was optimized using NSGA III to obtain the Pareto frontier, and the optimal solution was selected from the Pareto frontier using TOPSIS. The results showed that a suitable pilot injection strategy helped alleviate the problem of low cylinder pressure (CP) and high soot and HC emissions from the CI engine at high altitudes. The soot and HC emissions exhibited a decreasing and then increasing trend as the PIT advanced. As MRPI increased, both soot and HC emissions decreased. The NOx emissions showed the opposite trend. Compared with the non-optimized results, at an altitude of 2000 m, the optimized engine exhibited a 65.29% decrease in soot emissions, a 24.7% increase in NOx emissions, and a 74.94% decrease in HC emissions. Compared with the non-optimized results, at an altitude of 4000 m, the optimized engine demonstrated a 54.70% decrease in soot emissions, a 15.71% increase in NOx emissions, and a 65.78% decrease in HC emissions. This research will contribute to the application of oxygenated fuels in plateau diesel engines and the optimization of plateau diesel engines.

Optimizing combustion and emissions in natural gas/diesel dual-fuel engine with pilot injection strategy

For the clean and efficient operation of agricultural power, a non-road common-rail engine was modified to achieve natural gas/diesel dual-fuel (NDDF) combustion mode. Under low load conditions, NDDF combustion deteriorates and fuel economy decreases due to lower pressure and temperature inside the cylinder. Therefore, effects of injection pressure, pilot injection timing (SOIpilot) and pilot injection quantity (Qpilot) on in-cylinder combustion, emission characteristics and fuel economy of NDDF engine with pilot injection strategy were investigated at low load. Results show that with the increment of injection pressure, the diesel fuel beam penetration distance increased, prompting the diesel more quickly and fully mixed with fresh charge. The maximum in-cylinder pressure increased, the combustion center (CA50) moved forward, the ignition delay period was shortened, and soot, HC, C2H4 and C3H6 emissions were reduced, while BTE was improved. When SOIpilot moved forward, the pilot injected diesel and natural gas were more fully mixed, which promoted the generation of activation radicals and combustion intensity of main injected diesel. Pmax first increased and then decreased, the peak value of first heat release rate (HRRP1) gradually decreased, the peak value of second heat release rate (HRRP2) continuously increased, the combustion duration decreased, and the soot, CO and HC emissions decreased. At SOIpilot = −30 °CA ATDC, unregulated emissions reached the lowest level, while BTE was 35.55 %. With the increment of Qpilot, both Pmax and HRRP1 increased, CA05 and CA50 moved forward, combustion duration was extended, COV decreased significantly, and all emissions except NOx decreased, especially aldehyde emissions.

Influence of dwell time on the hydraulic behaviour utilizing multiple injection strategies and a piezoelectric diesel injector

The electric dwell time is defined as the duration between two electric pulse signals. It is a crucial parameter when multiple injection strategies are employed. The influence of electric dwell time on the hydraulic behaviour utilizing pilot injection strategy, split injection strategy, post injection strategy and a commercial piezoelectric diesel injector has been analysed experimentally. To do so, a sweep of electric dwell time from 1.15 ms up to 3 ms in all multiple injection strategies using rail pressures of 80, 100 and 120 MPa, and a back pressure of 5 MPa was performed. A fuel mass of 110 mg was injected in all cases analysed employing operating conditions defined from the characteristics curves of injected mass. The hydraulic behaviour was characterized through to measure the first and second hydraulic delay at opening and closing injector, the pressure oscillations generated during the first injection event, and injected fuel mass during second injection event in an injection discharge curve indicator, which is based on the Bosch tube method. In summary, the paper concludes that the hydraulic dwell time depends on the injected mass during the first injection event, and the dynamic response of injector. Moreover, a short electric dwell time causes an increase of injected fuel mass during second injection event, which can be attributed to combine two effects provoked by overlapping the first and second mass flow rate signals, namely, a reduction in the hydraulic delay at opening injector, and an increase in the hydraulic delay at closing injector. Finally, the present research provides information which can be employed to optimization the modulation of injection rate in a diesel engine.

Modeling the impact of the fuel injection strategy on the combustion and performance characteristics of a heavy-duty GCI engine

Gasoline compression ignition (GCI) is a promising strategy to achieve high thermal efficiency and low emissions with limited modifications to the conventional diesel engine hardware. It is a partially premixed concept, which derives its superiority from higher volatility and longer ignition delay of gasoline-like fuels combined with higher compression ratio typical of diesel engines. The present study investigates the combustion process in a GCI engine operating with different injection strategies using computational fluid dynamics (CFD). Simulations are carried out on a single cylinder of a multi cylinder heavy-duty compression ignition engine, which operates at a compression ratio of 17:1 and an engine speed of 1038 rev/min. Two different injection strategies viz., late injection (LI), and early pilot injection (EP) are investigated to understand their impact on combustion and performance of the engine. Renormalized group (RNG) k-ε model is used to describe in-cylinder turbulence and KH RT model is used to simulate the fuel spray breakup. The developed CFD methodology is validated against relevant experimental data under a wide range of operating conditions for each injection strategy. The developed CFD methodology was found to capture the engine combustion behavior quite well. Based on the validated CFD model, the differences in the progress of combustion event for the two injection strategies is highlighted. It was found that a larger pilot fuel mass fraction results in a steeper rise in the initial heat release rate which in turn influences the transition to mixing controlled combustion. In line with the experimental data, the study showed that the late pilot injection strategy with three injection pulses, results in higher performance compared to the other conditions.

Analysis of the performance and emissions generation mechanism of natural gas/diesel dual-fuel under different strategies by combining experiments and mechanisms

In natural gas/diesel dual-fuel engines, natural gas (NG) still produces some emissions during combustion, especially at high NG substitution rates. In order to reduce the emissions and to clarify the emissions formation mechanism. In this work, the performance and emission characteristics of the dual-fuel engine under different diesel injection strategies, as well as the formation mechanism of emissions (NOx, CO, THC and soot) were analyzed by combining bench test and chemical mechanism. The results showed that compared with diesel single injection, the diesel pilot injection strategy (PIS) could effectively improve the engine BTE (22.6%), CO and THC emissions were reduced by 87.8% and 76.1%, respectively. By advancing the diesel pilot injection timing (PIT), the combustion efficiency and BTE increased by 5.1% and 10.9%, respectively; the soot, THC, and CO emissions reduced by 63.9%, 69.4% and 76.9%, respectively. Increasing the diesel pilot injection ratio (PIR) could improve the combustion efficiency and reduce CO and THC emissions. According to the path analysis, the CO consumption was mainly the reaction R120: HO2+COOH + CO2, the generation of THC were mainly affected by path 1: CH3→CH3O→CH2O→HCO→CO and path 2: CH3→C2H6→C2H5→C2H4, and the soot was mainly related to C2H2, but it was mainly affected by the synergistic effect of multi-step reaction. Therefore, through the analysis of different diesel injection strategies, advanced the MIT and PIT of diesel and the medium PIR of diesel, the pressure and temperature of the engine were within the appropriate range, and the reactivity was kept in a good state, which could achieve low NOx, soot and THC emissions, high BTE and low BSEC from the engine.

Model predictive control of mixing controlled compression ignition operation for low reactivity fuels

Using gasoline or other low reactivity fuels with a pilot injection or port fuel injection in a compression ignition engine has shown great potential in reducing NOx emissions while keeping high thermal efficiency compared to diesel. However, excessive combustion noise is caused by a high maximum pressure rise rate in the cylinder due to the higher fractions of premixed charge of the low-reactivity fuel. This noise can result in structural damage to engine components and as such, combustion noise limits the range of the operating parameters and makes the control of such engines challenging. In this study, a simulation environment was built up in MATLAB/Simulink leveraging a physics-based zero-dimension combustion model to capture the in-cylinder pressure time traces as well as metrics relevant to thermal efficiency and combustion noise. In order to also facilitate the control of emissions, machine learning models were investigated to capture NOx emissions. A kernel-based extreme learning machine (K-ELM) performed best and had a coefficient of correlation (R-squared) of 0.998. The combustion and NOx emission models are valid for not only conventional gasoline fuel but also oxygenated alternative fuel blends at three different pilot injection strategies. In order to track key combustion metrics while keeping noise and emissions within constraints, a model predictive control (MPC) was applied for a compression ignition engine operating with a range of potential fuels and fuel injection strategies. The MPC is validated under different scenarios, including a load step change, fuel type change, and injection strategy change, with proportional–integral (PI) control as the baseline. The simulation results show that MPC reduces about 26% of ringing intensity in the transient process and 17% at the steady state for E30. Generally, MPC can optimize the overall performance through modifying the main injection timing, pilot fuel mass, and exhaust gas recirculation (EGR) fraction.

Numerical study on the effect of a two-stage pilot injection strategy on the performance of medium-speed diesel/natural gas dual-fuel marine engine

The need to reduce marine engine emissions continues to grow with the implementation of stricter emission standards. Numerical simulations were conducted to study the effect of a two-stage pilot diesel injection strategy on combustion and emissions in a medium-speed diesel/natural gas dual-fuel marine engine. A comprehensive analysis was performed on the start of the first pilot diesel injection (SOI1) and the proportion of the first pilot diesel injection (POI1), identified as two coupling factors of the injection strategy. The results indicated a significant improvement in indicated thermal efficiency (ITE) of over 48% and a reduction in nitrogen oxide (NOx) emissions of over 50% compared to the baseline single-stage injection strategy can be achieved through the use of high POI1 and delayed SOI1. In addition, the first pilot diesel spray covered the squish and piston bowl regions, enhancing the reactivity of the fuel-air mixture in these regions. The mass fraction of CH2O and H2O2 radicals determined the distribution of reactivity in different regions and characterized the transition process from low-temperature reaction to high-temperature reaction. The strategy of high POI1 and delayed SOI1 resulted in a better low-temperature reaction distribution, reducing combustion duration, improving ITE, and decreasing NOx, HC, CO emissions at medium load condition.

Environmental adaptability method for improving the cold start performance of the diesel engine based on pilot injection strategy

The deterioration of cold start performance at high altitudes is one of the main problems that restrict the altitude adaptability of diesel engines. In this study, by adapting the pilot injection strategy to improve cold start performance at different altitudes, the effect of the pilot injection ratio and pilot injection timing on the combustion, performance, and emission characteristics of diesel engines are investigated, and suggestions are proposed for optimizing fuel injection according to the altitude. The experimental results indicated that at high altitudes, the cold start performance was worse and more difficult to reach idle speed, NOx emissions increased due to the longer ignition delay. Compared to the single-injection strategy, the pilot injection strategy can effectively improve the combustion environment in the cylinder and thereby improve the cold start performance. As the altitude increase, decreasing the pilot injection mass can shorten the cold start time. The appropriate advance of pilot injection timing could improve mixture formation, which is conducive to improving the cold start performance and emissions at different altitudes. It can be concluded that advancing the pilot injection timing and increasing the pilot mass is a better injection strategy to improve cold start performance at plain. As the altitude increase, the pilot injection mass should decrease.

Effect of Pilot Injection Strategy on Performance of Diesel Engine under Ethanol/F-T Diesel Dual-Fuel Combustion Mode

To reduce emissions and save energy, alternative fuel and dual-fuel mode have been widely applied in the field of diesel engines. The pilot injection has potential to reduce engine vibration noise and pollutant emissions. The effects of a diesel fuel pilot injection strategy on the performance of an ethanol/F-T diesel dual-fuel engine were experimentally investigated on a four-cylinder four-stroke common rail diesel engine modified with an ethanol injection system. The results indicate that the variation in the combustion characteristic parameters with pilot injection timing is nonlinear and the difference is small, while soot, NOx, and CO tend to decrease, with an increase in pilot injection timing. With the increase in pilot injection amount, pmax, combustion duration, CO and soot increased; pmax phase and CA50 were closer to TDC; HRRmax and the ignition delay period decreased. The BSFC tends to increase with the increase in pilot injection timing and the increase in pilot injection amount, while the BTE shows the opposite trend. The value and the variation range of COVpmax are small. The effect of the pilot injection amount on ethanol/F-T diesel dual-fuel engine is more significant. The research presented in this paper can provide reference directions for the formulation of a fuel injection strategy of ethanol/F-T diesel dual-fuel combustion mode to reduce NOx without worsening the combustion process and presenting an insufficient fuel economy.

Zero Dimension Heat Release Modeling for Gasoline, Ethanol, Isobutanol and Diisobutylene Operating in Compression Ignition with Varying Injection Strategies

<div class="section abstract"><div class="htmlview paragraph">Gasoline compression ignition shows great potential in reducing NOx and soot emissions with competitive thermal efficiency by leveraging the properties of gasoline fuels and the high compression ratio of compression ignition engines operating air-dilute. Meanwhile, its control becomes challenging due to not only the properties of different gasoline-type fuels but also the impacts of injection strategies on the in-cylinder reactivity. As such, a computationally efficient zero-dimension combustion model can significantly reduce the cost of control development. In this study, a previously developed zero-dimension combustion model for gasoline compression ignition was extended to multiple gasoline-type fuel blends and a port fuel injection/direct fuel injection strategy. Tests were conducted on a 12.4-liter heavy-duty engine with five fuel blends. A modification was made to the functional ignition delay model to cover the significantly different ignition delay behavior between conventional and oxygenated fuel blends. The parameters in the model were calibrated with only gasoline data at a load of 14 bar brake mean effective pressure. The results showed that this physics-based model can be applied to the other four fuel blends at three different pilot injection strategies without recalibration. For all tests, the error of the maximum pressure is within 14 bar, and that of combustion phasing and indicated mean effective pressure is within 2 CAD and 1.1 bar, respectively. In addition, the model was validated with 7 bar BMEP data and had the same level of accuracy as the 14 bar cases.</div></div>

Experimental Evaluation of Pilot and Main Injection Strategies on Gasoline Compression Ignition Engine—Part 1: Combustion Characteristics

<div>Climate change and stringent emission regulations have become major challenges for the automotive sector, prompting researchers to investigate advanced combustion technologies. Gasoline compression ignition (GCI) technology has emerged as a potential solution, delivering higher brake thermal efficiency with ultra-low nitrogen oxides (NOx) and particulate emissions. Combustion stability and controls are some of the significant challenges associated with GCI. This study investigates the combustion characteristics of a two-cylinder diesel engine in GCI mode. GCI experiments were performed using a low-octane fuel prepared by blending 80% (v/v) gasoline and 20% (v/v) diesel (G80). Baseline experiments were conducted in conventional diesel combustion (CDC) mode. These experiments investigated the effects of double pilot injection, first pilot fuel ratio, and the start of main fuel injection timing (10–8°CA before top dead center, bTDC). The results indicated that the GCI mode produced significantly lower (~10%) in-cylinder pressure than the CDC mode. Higher pilot fuel proportions exhibited a lower heat release rate (HRR) at low loads. Retarded main injection showed a lower heat release in the premixed combustion phase than the advanced main injection case at all loads. In addition, retarded main injection timing showed retarded start of combustion (SoC) and end of combustion (EoC). GCI mode exhibited higher cyclic variations than baseline CDC mode, which need to be addressed.</div>

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>

Potential of ammonia energy fraction and diesel pilot-injection strategy on improving combustion and emission performance in an ammonia-diesel dual fuel engine

Ammonia (NH3) acting as a hydrogen carrier and carbon-free fuel has gotten more attention to reduce the carbon emissions from transportation. Ammonia-diesel dual-fuel combustion mode is one of the potential ways to achieve lower carbon emissions in compression ignition engines. However, NH3 and nitrous oxide (N2O) emissions were problems to reduce greenhouse gas emissions in this combustion mode. In this study, a diesel pilot-injection strategy where the pilot-injection energy ratio (PER) varied from 0 to 100% was used in an attempt to improve combustion and emission performance. In addition, ammonia energy ratios (AER) of 40%, 50%, 60%, and 70% were applied to this strategy to verify the feasibility of the pilot injection of diesel. Results showed the pilot-injection strategy could reduce NH3 emission from about 8000 ppm to 1000 ppm, and the reduction effect became more significant as the PER increased, while N2O emission also decreased at higher PER. Furthermore, the pilot-injection strategy could keep a high indicated thermal efficiency of about 45%. The engine achieved stable combustion at the wide AER region with low carbon dioxide (CO2) emission. However, higher nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbon emissions were disadvantages in the pilot-injection strategy.

Effect of Pilot Injection with Various Starts of Second Injection Command (SOIC2) and Fuel Injection Pressures on Gasoline Compression Ignition Combustion

This experimental study was conducted using a single-cylinder compression ignition (CI) engine with a pilot injection strategy to determine the effect of fuel injection pressure and the timing of the second start of injection (SOI2) on combustion and emission characteristics. This experiment used a mixture of 80% commercial gasoline (G80%) and 20% soybean biodiesel (B20%), by volume. The pilot injection strategy was applied with varying SOI2. Meanwhile, the first start of injection (SOI1) was constant at -350° ATDC and 900 bar fuel injection pressure. A range of fuel injection pressures from 400 to 900 bars and varied injection timing from -44 to -36 CA ATDC was applied at SOI2 to analyze the effect of injection timing and injection pressure on combustion characteristics and emissions. The increasing fuel injection pressure of GB20 in early injection timing will cause a longer ignition delay. The autoignition resistance of GB20 and the improvement of spray velocity enhance the wall wetting probability, consequently reducing the autoignition capability as fuel deposits were formed in the cylinder wall vicinity. Closer injection timing to TDC inhibits spray penetration due to higher room pressure and density, causing lower ignition delay. For GB20, 700 bar fuel injection pressure became the turning point in the ignition delay due to a lower fuel penetration velocity as a higher fuel injection pressure was applied. NOx emissions were identified as a sign of high temperature produced during combustion. The lowest CO2 emissions and the longest ignition delay appeared at the 700-bar injection pressure. Because incomplete combustion resulted in fuel deposits in the vicinity of the cylinder and temperature decrease, injection timings earlier than 40°CA BTDC initiated low thermal reaction (LTR) conditions, causing a temperature decrease during combustion.

Effects of EGR on combustion and emission characteristics of PODE/methanol RCCI mode at high load

In order to extend the high-load operation range of polyoxymethylene dimethyl ethers (PODE)/methanol dual-fuel reactivity controlled compression ignition (RCCI) combustion mode, a numerical model of in-cylinder combustion was established by coupling PODE/methanol chemical reaction kinetics with CONVERGE software. And then the influence mechanism of exhaust gas recirculation (EGR) addition on in-cylinder combustion process, combustion stability and pollutant formation of the RCCI engine under high load and pilot injection strategy were investigated. The results show that with the increase of EGR ratio, the peak values of the first heat release formed by PODE pilot injection combustion and in-cylinder pressure decrease, the combustion start timing and CA50 phase are gradually delayed. While the peak value of the second heat release formed by PODE main injection combustion at low EGR ratio and the combustion duration remain unchanged. Meanwhile, as the EGR ratio increases from 0 to 30 %, the brake thermal efficiency (BTE) decreases from 46.54 % to 44.40 %. And the in-cylinder equivalent ratio and temperature field distributions become uniform, and both high-temperature region (above 1800 K) and NOx generation area are reduced, which decreases NOx emissions by 42.6 % without increasing soot emissions. The methanol mixture at squish zone is subjected to the high-temperature and high-pressure of pilot injection combustion, resulting in obvious pressure oscillation. While EGR addition decreases the generation of HCO and OH active radicals, ignition points and reaction rate, which effectively inhibits methanol spontaneous combustion and knock phenomenon, and decreases the ringing intensity from 2.82 MW/m2 to 1.50 MW/m2. The pilot injection strategy coupled with 18 % EGR can extend the indicated mean effective pressure to 1.22 MPa. However, the load further extension is mainly limited by the sharp decline of BTE.

Effect of pilot injection strategy on the methanol-mineral diesel fueled reactivity controlled compression ignition combustion engine

Amongst all low-temperature combustion (LTC) strategies, reactivity-controlled compression ignition (RCCI) combustion garners more debate from researchers because of its excellent combustion and performance characteristics and lower emissions over a wide operating range. In this experimental investigation, the consequences of the start of diesel injection (SoIdiesel) timing using different pilot injection techniques, such as single and double pilot injection (SPI and DPI, respectively), have been investigated. Tests were performed at a fixed engine speed and load (1500 rpm and 3 bar BMEP, respectively) using different premixed ratios (rp: 0, 0.25, 0.50, and 0.75) of methanol on an energy basis. Experimental results indicated that the start of combustion (SoC) and combustion phasing (CP) advanced with advancing SoIdiesel. However, too advanced and retarded SoIdiesel timings resulted in combustion noise and misfire. The use of pilot injection was found suitable for the RCCI mode, especially at lower rp. However, SPI and DPI strategies didn’t show significant variations in the combustion characteristics. Exhaust gas temperature (EGT) showed a random trend with SoIdiesel timing, and it decreased with the increasing number of pilot injections. RCCI mode produced higher hydrocarbon (HC) and carbon monoxide (CO) and lower oxides of nitrogen (NOx) emissions. All these gaseous emissions decreased with advancing the SoIdiesel. Particulate matter (PM) analysis showed that the RCCI mode emitted relatively lower PM than the baseline CI mode, further reducing with increased methanol fuelling. PM emissions also decreased by retarding SoIdiesel, in which reduction in smaller particles was dominant. The analysis of critical parameters such as brake thermal efficiency (BTE), HC, NOx, and PM emissions suggested that the optimum rp of methanol and suitable injection strategy can significantly improve the combustion, performance, and emissions characteristics of the RCCI mode.

Effect of diesel/PODE/ethanol blends coupled pilot injection strategy on combustion and emissions of a heavy duty diesel engine

Ethanol has limited solubility in diesel. Polyoxymethylene dimethyl ethers (PODE) can enhance the miscibility of ethanol/diesel blends. The application of pilot injection strategy can improve combustion noise and NOx emissions. Thus, the effects of different diesel/PODE/ethanol blends coupled various pilot injection strategies on the combustion, performance and emissions were conducted in a six-cylinder heavy duty diesel engine. As renewable alternative fuel, PODE has the characteristics of high cetane number, high oxygen content and no CC bond, while ethanol has the characteristics of high volatility and high oxygen content. The results show that the significant differences in heat release rate (HRR) and maximum pressure rise rate (MPRR) among DP20, DPE5, DPE10 and DPE15 can be reduced by using the pilot injection, in that the differences in HRR timing and peak value of HRR are weakened. Both the brake and indicated thermal efficiency of blends can be improved by appropriately optimizing the pilot strategy, when compared with the case of single injection. The thermal efficiency of blends is more sensitive to the pilot injection quantity, while the CO and HC emissions are more sensitive to the pilot-main interval. For single injection, blending ethanol into PODE/diesel blends causes adverse effects of increasing hazardous gas emissions, while optimizing pilot injection strategy can reduce the hazardous gas emissions of the blends to the best level of diesel and significantly reduce soot emissions when compared to diesel.