Pilot Injection Timing Research Articles

Improvements in thermal efficiency and exhaust emissions with ozone addition in a natural gas-diesel dual fuel engine

Here, ozone (O3) was introduced into the intake air in a natural gas fueled engine ignited by diesel fuel, a natural gas–diesel dual fuel engine, to utilize the reactive O-radicals decomposed from the O3 for the promotion of the ignition and for improvements in the thermal efficiency and exhaust emissions. The engine experiments were performed over a range of equivalence ratios of the natural gas in a single cylinder engine. The timing of the pilot injection of the diesel fuel was varied from early in the compression stroke to near top dead center to examine the changes in the effects of the O3 addition on the ignition and combustion with the pilot injection timing while varying the O3 concentration. The results showed that the combination of the O3 addition and the early pilot injection is a means to improve the thermal efficiency and unburned emissions with a small amount of O3. Further, the improvement in the thermal efficiency and the reduction of the unburned hydrocarbons with the O3 addition are more pronounced for lower equivalence ratios of natural gas, while the O3 addition has a limited effect on the thermal efficiency and the unburned hydrocarbons for higher equivalence ratios of the natural gas.

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>

Parametric investigation on the performance-emissions trade-off and knocking occurrence of dual fuel engines using CFD

Dual fuel (DF) engines have been an attractive alternative of traditional diesel engines for reducing both the environmental impact and operating cost. The major challenge of DF engine design is to deal with the performance-emissions trade-off via operating settings optimisation. This study aims at parametrically investigating the engine settings optimisation for a simultaneous reduction of NOx emissions and brake specific fuel consumption (BSFC) of marine DF engines while avoiding knocking accurrence by using a computational fluid dynamics (CFD) model. The model is developed in the CONVERGE software and validated by employing the measured in-cylinder pressure and emissions. Subsequently, the model is used to parametrically investigate the engine operating settings (pilot injection timing, equivalence ratio and natural gas mass) that allow simultaneous reduction of NOx and BSFC emissions at three engine operating conditions (1800 r/min, 1629 r/min and 1457 r/min). Result shows that the optimal solution at 1800 r/min and 1629 r/min operation conditions can be achieved by controlling the pilot injection timing, equivalence ratio variation and NG mass variation within –5 to –7.5 °CA, –5% to +5 % and 0 % to +20 %, respectively. For the 1457 r/min operation condition, the appropriate ranges of pilot injection timing and the equivalence ratio variation are the same with those at 1800 r/min and 1629 r/min, whilst the NG mass variation range should be between –10 % and +10 %. The derived results in this study are expected to support the combustion analysis and enhancement of marine DF engines during the design phase, whilst the derived optimal solution is expected to provide guidelines of DF engine management for reducing operating cost and environmental footprint.

Effects and mechanism of pilot diesel injection strategies on combustion and emissions of natural gas engine

The research objectives of pilot diesel injection (PDI) ignition natural gas technology include high efficiency, clean combustion, and low pilot diesel mass. This study is based on a single-cylinder thermodynamic engine, combined with the CONVERGE simulation model and CHEMKIN chemical reaction kinetics model. The effects and mechanisms of various PDI strategies on the mixture equivalent ratio, temperature, and characteristics of combustion and emissions were investigated. The experimental results showed that the best PDI mass was 8 mg/cycle. The thermal atmosphere and activity in the cylinder were improved with an increase in PDI mass from 2 to 8 mg/cycle, which stabilized the mixture combustion. Further, the effects of different pilot injection timing (PIT) on combustion and emissions were investigated via experiments and simulation by controlling the operating conditions and maintaining a constant PDI total mass. The results show that the diesel had a single low-temperature reaction path when the PIT was close to the top dead center, whereas the PIT at the early stage of the compression stroke (CS) changed the chemical reaction path and accelerated the transformation of CH3 to CH2O, accumulating numerous active groups and accelerating the combustion rate, which is difficult to control the ignition phase. The reaction path of the double PDI strategy was similar to that of the PIT at the early CS stage, and its combustion is closed to premixed combustion; however, the accumulation of active groups was relatively small, and the combustion rate was relatively slow because the ignition phase was controlled by the second PDI, making the combustion phase easy to control. Finally, with the double PDI strategy that had the advantages of efficient combustion and avoidance of knock, the gross indicated thermal efficiency reached 49.3% that involved a −60°crank angle (CA) after top dead center (ATDC) first injection and −4°CA ATDC second injection.

Effect of Cetane-Coupled Pilot Injection Parameters on Diesel Engine Combustion and Emissions.

The effects of cetane number (CN) coupled with pilot injection ratio and pilot injection timing on the combustion and emission characteristics of a four-cylinder diesel engine were investigated. The results showed that as the pilot injection ratio increases, the peak cylinder gas pressure (CGP) increases, and the peak of heat release rate (HRR) increases accordingly; the coupled CN increases, the brake specific fuel consumption (BSFC) decreases, and the brake thermal efficiency (BTE) increases; CO and HC emissions increase; and NO x emissions increase. In addition, the number concentration and total mass of particulate matter (PM) decrease with the increasing pilot injection ratio. Only when the pilot injection ratio reaches 20% does the fuel produce pilot injection heat release. The ignition delay time (ID) and combustion duration (CD) are redefined for the pilot injection heat release operating conditions. With the delay of the pilot injection timing, the peak CGP increases, the coupled CN increases, the BTE increases, the BSFC decreases, CO and HC emissions increase, and NO x emissions decrease. With the delay of the pilot injection timing, the number concentration and total mass of PM decrease. In addition, no pilot injection heat release was generated for any of the five fuels at pilot injection timings from 30°CA BTDC to 45°CA BTDC.

Combustion and emission characteristics of diesel engine fueled with diesel/cyclohexanol blend fuels under different exhaust gas recirculation ratios and injection timings

Cyclohexanol is obtained from abundant lignocellulosic biomass sources at low cost, and it is a promising alternative fuel for diesel engines. In this study, cyclohexanol was blended with diesel at various volume ratios and the mixtures were denoted as D100 (100 % diesel + 0 % cyclohexanol), D90CH10 (90 % diesel + 10 % cyclohexanol), and D80CH20 (80 % diesel + 20 % cyclohexanol), respectively. Subsequently, the effects of exhaust gas recirculation and pilot plus main injections at various pilot injection timings on the combustion and emissions of the diesel engine fueled with various mixtures were evaluated. The results demonstrated that diesel/cyclohexanol blends had a longer ignition delay, but shorter combustion duration. D80CH20 had the highest oxygen content, peak combustion temperature (PCT), and peak heat release rate (PHRR) at medium and high loads. Cyclohexanol blending with diesel significantly decreased the particulate number (PN) and volume concentrations at the expense of higher NOx emissions. Advancing the pilot injection timing prolonged the ignition delay and combustion duration, and increased the PCT and PHRR. Therefore, it emitted higher NOx emissions, but lower PN emissions. D80CH20 with 8 % EGR can simultaneously reduce the PN and NOx emissions at medium and high loads.

Application of pilot injection strategies for enhanced ignition and combustion of a low reactivity fuel in a compression-ignition engine

• Pilot injection can enhance combustion of a low reactivity fuel. • Pilot mixtures merging with main jet is a cause for studied mixture conditions. • Earlier pilot injection achieves enhanced reaction for studied mixture conditions. • Higher pilot proportion and shorter pilot-main dwell have higher effects. • HCHO formation is higher and its consumption to form OH is increased. The impact of pilot injection on ignition and combustion of a low-reactivity fuel is systematically investigated in an optically accessible light-duty compression-ignition engine. The role of key pilot-main injection control parameters, including the pilot injection timing, proportion and pilot-main injection dwell time, is found through line-of-sight integrated high-speed imaging of cool-flame and OH* chemiluminescence signals as well as planar laser-induced fluorescence imaging of formaldehyde (HCHO-PLIF) and hydroxyl (OH-PLIF). This suite of diagnostics enables visualisation of low-temperature reaction and high-temperature reaction during the extended ignition delay period of a selected low reactivity fuel with only 30 cetane number. The results show significant combustion enhancement associated with the pilot-main injection strategy for all injection timings tested. The enhanced ignition is most effective in the case of retarded injection timings with almost misfiring single injection operation recovered for stable and strong combustion due to the pilot mixture merged with the main fuel jet. This enhancement effect is further promoted when the proportion of pilot injection mass to the total fuel mass is increased or the dwell time between the pilot and main injection is decreased as the pilot mixture interaction with the main fuel jet is enhanced. Compared to the single injection, measured HCHO-PLIF signals are higher and OH-PLIF signals develop at a higher rate due to the pilot injection, indicating the pilot mixture addition enhanced both the low-temperature reaction and high-temperature reaction of the tested low-reactivity fuel.

The effect of diesel pilot injection strategy on combustion and emission characteristic of diesel/methanol dual fuel engine

The effects of diesel fuel pilot injection timing, pilot mass percent and methanol substitution rate on the combustion and emissions of a diesel-methanol dual fuel engine were experimentally investigated. The experiments were conducted on a single-cylinder, naturally aspirated common rail diesel engine modified with a methanol injection system. The results indicated that the addition of pilot injection advanced the ignition time and increased the heat release rate. With the advancement of pilot injection timing, the ignition delay increased, and the indicated thermal efficiency reduced. The NOx emission first decreased and then increased while the smoke emission showed the opposite trend. With the increase in the pilot mass percent, the peak in-cylinder pressure and the heat release rate increased. Meanwhile, the ignition time and the CA50 advanced. At different pilot injection timing, the combustion duration and the indicated thermal efficiency showed different trends. Meanwhile, with the increase in the pilot mass percent, the NOx emission increased and the smoke emission decreased. When the MSR increases from 20% to 40%, the indicated thermal efficiency increases by 1.9 percentage points, and the NOx and smoke emissions decrease by 88% and 61% respectively by advancing the PIT and increasing the pilot mass percent with the EGR combined. It can be concluded that, at high MSR, advancing the pilot injection timing and increasing the pilot mass percent with EGR combined is a better injection strategy to improve the performance of combustion and emissions.

Influence of Pilot Injection on Combustion Characteristic of Methanol–Diesel Dual-Fuel Engine

An experimental study regarding methanol–diesel dual-fuel (DF) engines was conducted on a modified engine to explore the effects of pilot injection timing and period on the two-stage combustion process caused by the pilot injection strategy. In this study, the two-stage combustion process was determined according to the first two peaks of the second derivative of an in-cylinder pressure (d2p/dφ2) curve. The results show that the peak pressure rise rate (PRR) tended to decrease with advancing pilot injection timing at a high co-combustion ratio (CCR), which reduced combustion noise. The start of the combustion of the main injection diesel (SOC2) could be advanced by increasing the pilot injection period or advancing pilot injection timing at a 42% CCR. At an 18% CCR, the pilot injection timing and period had no significant effect on SOC2. With the advancement of pilot injection timing, the start of the combustion of pilot injection diesel (SOC1) advanced, and generally, the coefficient of variation of the PRR (COVPRR) of the two-stage combustion process increased first and then decreased. However, with the increase in the pilot injection period, SOC1 almost always remained constant and the COVPRR of the two-stage combustion process generally increased.

Effect of injection timing on combustion, emission and particle morphology of an old diesel engine fueled with ternary blends at low idling operations

Currently, idling emissions and old vehicle emissions have attracted more and more attention. Many countries have made corresponding policies to limit these emissions. In this study, to investigate the combustion, engine performance, and emission characteristics of an old diesel engine fueled with diesel-palm biodiesel-ethanol (DPE) ternary blended fuels according to various multiple injection strategies under low idling conditions, a series of experiments were carried out on an old common-rail direct injection (CRDI) diesel engine. The engine speed and load were fixed at 750 rpm (the lowest speed) and 30 Nm, respectively. Two test modes of A (only pilot injection timing was variable) and B (only main injection timing was variable) were comparative studied. The experimental results show that the main-pilot injection timings and DPE ternary blends have significant impacts on the engine performance, combustion and characteristics. Overall, as the ethanol concentrations in DPE ternary blends increase, brake specific fuel consumption (BSFC), maximum heat release rate (HRRmax), ignition delay, carbon monoxide (CO) and hydrocarbon (HC) emissions increase, while nitrogen oxides (NOx) and smoke emissions are simultaneously reduced. The high volatility, high latent heat of evaporation and high oxygen content of ethanol may play a major role in reducing NOx and smoke emissions. In addition, the primary particle diameter of all tested fuels is distributed in a narrow range of 18–24 nm, and the addition of ethanol is beneficial to reduce the particle diameter.

Exploring the effects of pilot injection timing and natural gas flow rates on the performance of twin-cylinder compression ignition engine

ABSTRACT Alternative fuels offer various advantages over traditional fossil fuels, including the fact that they are recyclable, sustainable, Contribute to energy independence, and reduce emissions. Renewable fuels such as Compressed natural gas and biodiesel were used in this study. Natural gas is an appealing and appealing fuel because of its vast availability, low Cost, and Clean-burning qualities. The use of biodiesel, namely mustard oil biodiesel, aids in making it Cleaner and more Cost-effective. The present study aims to reduce tailpipe emissions from diesel engines using dual-fuel Combustion, which employs a Combination of fossil and renewable fuels. An experimental analysis was Carried out to evaluate the effectiveness and tailpipe emissions of a twin-cylinder diesel engine fueled by pilot Mustard oil biodiesel (MOB) and CNG, with variations in the rate of CNG flow and time of pilot injection. According to the findings, advanced pilot injection timing (PIT) at 24°CA bTDC (degree Crank angle before top dead Center) and using a lower rate of CNG flow (0.2 kg/h) resulted in the highest brake thermal efficiency (31.21%), while brake specific fuel Consumption decreased by nearly 10% at this setting. Increasing pilot fuel injection to 24°CA bTDC and maintaining a modest rate of CNG flow at 0.2 kg/h in a dual-fuel model decreased NOx emissions by 26% when Compared to diesel alone mode, but resulted in a minor rise in CO emissions. The Current study may aid in the Conversion of a significant number of small to mid-segment diesel engines used in irrigation and the industrial sector in the Indian subcontinent. The study helps in minimizing NOx emissions while also lowering import fossil fuel Costs.

Synergistic effect of post injection and CART unit in extenuating Tail-Pipe pollutants in CI engine using C. pyrenoidosa microalgae biodiesel

The objective of this study is to control particulate smoke emissions (PSE) and harmful greenhouse gases (GHG) using post injection-activated continuous active regeneration trap (CART)at maximum throttle pedal position (MTPP) condition while operating on C. pyrenoidosa microalgae biodiesel (CP20D80). Furthermore, the CART unit efficiency is analyzed based on its ability to mitigate the harmful emissions without sacrificing the engine performance characteristics. From the study, while operating on CP20D80, the maximum de-smoke and de-HC CART efficiency of 67.85% and 67.25% is observed at the pilot injection timing (PIT) of 20°CA aTDC and 15°CA aTDC and at a post injection mass (PIM) of 4 mg and 1 mg for low and high load condition. In all cases, elimination of CO emissions and simultaneous reduction of PSE and NOX emission is observed to an extent despite the lower de-NOX efficiency of the CART unit at all PIT and PIM. However, the least BSFC and maximum BTE was observed for diesel fuel which is 2.7% lesser and 3.7% more than CP20D80 at a PIM of 1 mg and PIT of 20°CA aTDC and 10°CA aTDC under high load condition.

Effect of split injection strategies on diverse characteristics of a common rail direct injection diesel engine operating with diesel-palm oil-ethanol micro-emulsions

This study investigated the effect of pilot injection timing (PIT) and pilot injection quantity (PIQ) on the performance of a common rail direct injection (CRDI) diesel engine with two-stage injection system operating with diesel-palm oil-ethanol micro-emulsions. The results indicated that, at low engine load, the maximum in-cylinder pressure (Pmax) and peak of heat release rate (HRR) of D35P35E30 were highest, and those of D100 were lowest. At high engine load, the Pmax of D100 was highest, that of D60P30E10 was lowest, and the peaks of HRR were almost identical for all test fuels. The Pmax and peak of HRR were slightly increased with the advance of PIT. Increasing PIQ increased the first peak of HRR and reduced the second one. At low engine load, the coefficient of variation (COV) of Pmax and the indicated mean effective pressure (IMEP) presented a slight decrease for the micro-emulsions, but did for D100 at high engine loads. The brake specific fuel consumption (BSFC) of the micro-emulsions was higher, and the brake thermal efficiency (BTE) was also slightly higher when compared with diesel (D100). With the advance of PIT and the increase of PIQ, BSFC was increased, BTE was decreased, and hydrocarbon (HC) emissions were reduced. The variation of PIT and PIQ had little effect on the particle number concentration (PNC), but had evident effect on nitrogen oxides (NOx) emissions. It was concluded that the micro-emulsions can be used to reduce NOx and particulate matter (PM) simultaneously combined with injection strategy in a diesel engine.

Impact of exhaust gas recirculation and split injection strategy combustion behavior on premixed charge compression ignition engine fuelled with moringa oleifera methyl ester

Influence of split injection strategy of moringa oleifera methyl ester and its blends with exhaust gas recirculation on diesel engine combustion, performance and emission characteristics using common rail direct injection (CRDI) system were investigated in this work. In split injection strategy, the pilot (PIT) and main injection timings (MIT) were fixed between 35 °CA – 40 °CA bTDC and 15 °CA –25 °CA bTDC, respectively. The minimum and maximum nozzle opening pressure were fixed as 300 and 600 bar with an interval of 100 bar. In addition, 10% to 30% of EGR flow rate was introduced with an interval of 5%. Experimental results reveal that B100-10%-90% has achieved maximum brake thermal efficiency of 35% at PIT of 35 °CA bTDC, MIT of 25 °CA and NOP of 300 bar. Usage of pure moringa oleifera biodiesel in diesel engine under split injection strategy results in better combustion characteristics due to premixed and diffused heat release rate phasing with lower peak cylinder pressure. In addition, B100-10%-90% emits maximum nitric oxide emission of 1520 ppm, and least unburned hydrocarbon and carbon monoxide emission of 4 ppm and 0.01% vol respectively at 600 bar NOP with PIT of 35 °CA and MIT of 25 °CA. Moreover, Nitric oxide emission is reduced as the EGR rate gradually increases from 10% to 30%; on the other side, brake specific fuel consumption, carbon monoxide, and unburned hydrocarbon emissions are marginally increased. This research depicts that split injection strategy and EGR technique have simultaneously lowered the nitric oxide and smoke emissions while improving engine performance.

Energy balance analysis of a DI diesel engine with multiple pilot injections strategy and optimization of brake thermal efficiency

• Timing and quantity changes of two pilot injections were applied to diesel engine. • The effects of each change on total fuel energy distribution were investigated. • 2nd PiI quantity change has the strongest effect on components of total fuel energy. • 2nd PiI timing change has the least effect on components of total fuel energy. • NSGA-III optimization maximized brake thermal efficiency with an increase of 0.29%. • An increase of 0.74% was obtained in the total exhaust energy percentage which is recoverable. In this study, multiple pilot injections (MPI) strategy having two pilot injections was applied to direct injection (DI) diesel engine running at partial load which is usually within legal emission cycle. Optimization of timing and quantity of the pilot injections is a key factor in achieving performance and emission targets. Due to the advantages of pilot injections in terms of smooth and gradual release of energy from the fuel, the energy distribution in the engine has been put under scope and investigated thoroughly. The effects of varying the timing and quantity of both pilot injections within a reasonable range on brake thermal efficiency, total exhaust energy, in-cylinder heat transfer and friction were investigated and results were presented using a well calibrated and validated thermodynamic model. Relative sensitivity analysis and Spearman correlation coefficients analysis were performed to show the effects of each MPI parameter on the total fuel energy components. The variation of 2nd pilot injection quantity determined the most influential parameter on brake thermal efficiency with a relative sensitivity value of 0.4612, on in-cylinder heat transfer with a relative sensitivity value of 0.4708, on total exhaust energy with a relative sensitivity value of 0.4757 and on friction power with a relative sensitivity value of 0.4677 respectively. Similar to the variation in the 2nd pilot injection quantity, the variation in the 1st pilot injection quantity affected these responses in the same way but with less effect. Timing variations in both pilot injections were found out to be the third and the fourth parameters affecting responses. Especially the variation in 2nd pilot injection timing has the least effect on components of total fuel energy. Retarding both pilot injections increased the brake thermal efficiency and the variation of both pilot injection timing has similar effect on brake thermal efficiency. Retarding the 1st pilot injection timing augmented the total exhaust energy while reducing the in-cylinder heat transfer to coolant and friction power. Non-dominated Sorting Genetic Algorithm-III (NSGA-III) optimization tool was used for finding the optimal timing and quantity of both pilot injections to maximize brake thermal efficiency. A growth of 0.29% at a rate of %1 in the brake thermal efficiency was achieved. Additionally, an increase of 0.74% at a rate of 2.4% in the total exhaust energy has the potential to be used and recovered in the turbine.

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

In order to explore the optimization scheme of injection strategy for dual-fuel engine at low load, diesel/methanol dual-fuel combustion mode was conducted on a turbocharged intercooled engine. Effects of methanol ratio, main and pilot injection parameters on combustion process, emission characteristics and fuel economy of dual-fuel engine were systematically studied at 30% load of 1800r/min. Results show that with the addition of pilot injection strategy, dual-fuel combustion process gradually changed from two-stage to single-stage with methanol ratio increasing, the upper limit of methanol ratio was increased from 40% to 60%, the cyclic coefficient of variation (COV) and HC emissions decreased, and the brake thermal efficiency (BTE) increased. While the heat release was delayed with the advance of pilot injection timing, the peak heat release rate increased, and the combustion duration, soot emission and COV decreased. Additionally, the increasing pilot injection quantity would make heat release rate curve evolve to bimodal distribution, resulting in advanced CA05 and CA50, and the increased BTE, NOx and soot emissions along with the decreased HC and CO emissions were also observed. Dual-fuel engine with optimized pilot/main injection strategy could achieve the BTE of 47.34% and the COV of 1.4% at 50% methanol ratio condition.

Computational study of diesel injection strategies for methane-diesel dual fuel engine

Methane-diesel dual fuel engine is an effective solution for partial replacement of conventional diesel fuel and pollutant reduction in compression ignition engine. However, it has several challenges from the large scale market acceptability perspective such as low combustion and thermal efficiency and high hydrocarbon (HC) and carbon monoxide (CO) emission. These problems can be addressed with the optimization of injection strategies of diesel fuel. The present work explores the effect of diesel injection strategies on combustion, performance and emission characteristics of methane-diesel dual fuel engine. Firstly, injection timing of diesel fuel is varied for single injection case. After that split injection strategy is explored with varying pilot mass amount (15%, 30% and 45%) and varying pilot injection timing (12°bTDC to 30°bTDC) at fixed main fuel injection timing (8°bTDC). The results revealed that 8°bTDC injection timing is obtained as optimum injection timing for single injection case for methane-diesel dual fuel engine from enhanced performance, combustion and reduced emissions point of view. In case of split injection, advancement of pilot injection (SOI1) timing till 24°bTDC decreased the methane slip, HC and CO emissions. SOI1 timing earlier to 24°bTDC increased the methane slip, HC and CO emissions for all pilot mass injections (15, 30 and 45%). Higher pilot mass injection resulted in higher methane slip, HC and CO emission in SOI1 range of 24–30°bTDC. SOI1 timing exhibited different trends of soot and NO x emission with different pilot mass injection. GTE reduced with advanced SOI1 injection timing. Overall, with split injection technique, 24°bTDC is optimum pilot injection (SOI1) timing, and 15% pilot mass amount is optimum amount and 8°bTDC is optimum main injection (SOI) timing for methane-diesel dual fuel engine. • Effect of diesel injection strategies on characteristics of methane-diesel dual fuel engine. • Single injection as well as split injection have been investigated. • For single injection case 8°bTDC is found as optimum timing. • In split injection, injection timing were varied from 12°bTDC to 30°bTDC. • Pilot injection amount (15%, 30% and 45%) were also varied.

Multiple fuel injection strategy for premixed charge compression ignition combustion engine using biodiesel blends

In the last decade, advanced combustion techniques of the low-temperature combustion (LTC) family have attracted researchers because of their excellent emission characteristics; however, combustion control remains the main issue for the LTC modes. The objective of this study was to explore premixed charge compression ignition (PCCI) combustion mode using a double pilot injection (DPI; pilot-pilot-main) strategy to achieve superior combustion control and to tackle the soot-oxides of nitrogen (NOx) trade-off. Experiments were carried out in a single-cylinder research engine fueled with 20% v/v biodiesel blended with mineral diesel (B20) and 40% v/v biodiesel blended with mineral diesel (B40) vis-à-vis baseline mineral diesel. Engine speed and rate of fuel-mass injected were maintained constant at 1500 rpm and 0.6 kg/h mineral diesel equivalent, respectively. Pilot injection timings (at 45° and 35° before top dead center (bTDC)) and fuel quantities were fixed, while three fuel injection pressures (FIPs) and four different start of the main injection (SoMI) timings were investigated in this study. Results showed that multiple pilot injections resulted in a stable PCCI combustion mode, making it suitable for higher engine loads. For all test fuels, advancing SoMI timings led to relatively lesser knocking; however, engine performance characteristics degraded at advanced SoMI timings. B40 exhibited relatively superior engine performance among different test fuels at lower FIP; however, the difference in engine performance was insignificant at higher FIPs. Fuel injection parameters showed a significant effect on emissions, especially on the NOx and particulates. Advancing SoMI timing resulted in 20%–50% lower particulates emissions with a slight NOx increase; however, the differences in emissions at different SoMI timings reduced at higher FIPs. Somewhat higher particulates from biodiesel blends were a critical observation of this study, which was more dominant at advanced SoMI timings. Qualitative correlation between NOx-total particulate mass (TPM) was another critical analysis, which exhibited the relative importance of different fuel injection parameters for other alternative fuels. Overall, B20 at 700 bar FIP and 20° SoMI timing emerged as the most promising proposition with some penalty in CO emission.

Effects of pilot injection strategy on in-cylinder combustion and emission characteristics of PODE/methanol blends

Polyoxymethylene dimethyl ethers (PODE) and methanol are both promising alternative fuels with high oxygen content, and the combustion and emission characteristics of PODE/methanol blends were investigated in a common-rail engine. The premixed charge compression ignition (PCCI) combustion was realized by appropriate match of main injection and pilot injection strategies. The effects of methanol ratio (0– 20%) on fuel economy and emissions formation were studied in conventional compression ignition (CI) and PCCI modes. The combustion and emission characteristics were improved by adjusting the pilot injection timing (−40 ~ −24 °CA ATDC) and pilot injection ratio (0– 20%). The results show that the increase of methanol ratio prolongs the ignition duration, increases the premixed combustion ratio and reduces NOx emissions. PCCI combustion increases the brake thermal efficiency (BTE) and improves the trade-off relationship between NOx and soot. The delay of pilot injection timing increases the BTE, decreases HC, CO and HCHO emissions, but increases NOx and soot emissions. The appropriate pilot injection ratio can significantly increase the BTE, and has little effect on the emission characteristics. Under the optimized pilot injection strategy and appropriate methanol ratio conditions, the maximum BTE of the blends can reach 46.58% and maintain low emission level.

Data Driven Feedforward Control Strategy for Multi-Fuel UAS Engine

An engine is a complex system that requires a control strategy to perform optimally and reliably. The majority of the existing system uses a lookup table-based control strategy, also known as feedforward tables, generated offline by performing engine calibration, which is usually an expensive process. The calibration cost can be significantly reduced using a system model, but due to the increased engine complexity, developing a physics-based model that can capture all the system modes becomes challenging. Therefore, the current work uses a data-driven approach to model a diesel engine and designs its control strategy based on it. It uses Gaussian Process Regression (GPR) to model the engine and perform system inversion to achieve the desired optimal feedforward control. Two control inputs, namely, pilot injection timing (PIT) and main injection timing (MIT), are calculated to achieve the desired combustion performance in terms of CA50 from the engine. Model inversion is done using the real-variable genetic algorithm (rGA) to obtain the optimal control strategy corresponding to the desired CA50. The study tries to address two fundamental issues for developing a data-driven control strategy for a practical system: when the model is developed using limited number of data points, and the inversion problem when multiple control settings generate the same optimal output. Finally, the proposed control strategy is validated on an actual experimental test bench, and the results show excellent performance in achieving the desired CA50 value.