Ignition Mode Research Articles

A DNS study of ignition characteristics of a lean PRF/air mixture with [formula omitted]O and H[formula omitted]O[formula omitted] addition under HCCI combustion-relevant conditions

The effects of additive injection including CH2O and H2O2 on the ignition characteristics of a lean primary reference fuel (PRF)/air mixture under homogeneous-charge compression ignition (HCCI) combustion conditions are investigated using 2-D direct numerical simulations (DNSs) with a 116-species reduced chemical mechanism. The 2-D DNSs of HCCI combustion are performed by varying the type and amount of the additives with a pseudo-species model and a compression-heating/expansion-cooling model. It is found that the first-stage and main ignitions are retarded by CH2O addition while the latter is promoted by H2O2 addition. By adjusting the amounts of dual additives, the main ignition can be manipulated to occur at a specific time similar to that with no additives while its mean heat release rate becomes more distributed over time than that with no additives. Combustion mode analysis reveals that a mixed mode of combustion occurs during the late phase of HCCI combustion with CH2O addition or dual additives, while spontaneous ignition mode of combustion is predominant for cases with H2O2 addition or no additives. Displacement speed analysis also verifies that CH2O addition induces deflagration rather than spontaneous ignition at the reaction fronts, which consequently leads to a smooth ignition of the RPF/air mixture. In addition, chemical explosive mode analysis (CEMA) identifies important variables and elementary reactions for low-, intermediate-, and high-temperature chemistries for the ignition of PRF/air mixture with and without additives.

Characterization of CNG induced transition regimes of reactivity-controlled-combustion of Madhuca longifolia biodiesel: An experimental case study

ABSTRACT This study demonstrated the synergistic capability of split-injection techniques to achieve the better emission-performance-stability endeavor of a diesel engine operating under CNG-biodiesel reactivity-controlled compression ignition (RCCI) mode. CNG will enhance a diesel engine’s performances characteristics and reduce emissions when combined with a split injection technique. The biodiesel yielded from Mahua oil was characterized by Gas Chromatography-Mass spectrometry (GC-MS) analysis and classified biodiesel components. However, various physical properties were determined from GC-MS analytical responses. A systematic split-injection effort was tested for each pilot, and the main injection at different angles fueled with CNG-biodiesel to achieve the RCCI mode of combustion. The variance coefficient for indicated mean effective pressure (COVIMEP) data demonstrated more reliable engine operation when fueling with CNG-biodiesel instead of fossil diesel. The analysis showed the highest exergy efficiency (30%) and the lowest brake specific energy consumption (8.64%) as performances characteristics, reported for RCCI mode of operation. This experimental study showed the lowest value of NOx, Soot, and UHC emissions under RCCI regimes. These values of NOx, Soot, and UHC emissions are 21.4%, 33.4%, 50% higher than plain biodiesel operation and 75.28%, 21.29%, and 83.87% better than plain fossil diesel operation. Therefore, the analysis showed the synergistic advantages of a CNG-biodiesel RCCI engine operating with the split injection mode to achieve higher efficiency and lower emission characteristics.

On the flame stabilization of turbulent lifted hydrogen jet flames in heated coflows near the autoignition limit: A comparative DNS study

Three-dimensional direct numerical simulations of turbulent lifted hydrogen jet flames in heated coflows are performed with a detailed H2/air chemical mechanism to understand their ignition dynamics and stabilization mechanisms. Turbulent lifted jet flames with four different coflow temperatures, Tc, between 750 K and 1100 K are investigated by examining the instantaneous/time-averaged values and conditional means of heat release rate and species critical to ignition, and by performing a displacement speed analysis and a local combustion mode analysis with an indicator, α. Although Tc at 950 K is higher than the autoignition limit, the flame is primarily stabilized by flame propagation rather than autoignition, while at 1100 K, flame stabilization is found to be highly affected by autoignition. The local combustion mode analysis further reveals that at 950 K, even if a local ignition mode with |α|<1 first appears in the near field of the jet, it develops into a local extinction mode with α<−1 as local temperature decreases due to the excessive mixing of heated coflow and cold H2 within vortical structures, which inhibits the ignition kernel development upstream of the flamebase. At 1100 K, however, a local ignition mode prevails upstream of the flamebase. To further identify the effect of a vortex on the early development of an ignition kernel in a mixing layer between the heated coflow and cold H2, a series of two-dimensional DNSs are performed, varying several vortex parameters and air temperature, as a reference for the more complicated corresponding 3-D turbulent DNS cases. The results substantiate that the development of a vortex in the mixing layer tends to retard the autoignition within the vortex, especially when its temperature is slightly above the autoignition limit.

The correlation between intake fluctuation and combustion CCV (cycle-to-cycle variations) on a high speed gasoline engine: A wide range operating condition study

In this work, the cycle-to-cycle variations (CCV) and their correlations to intake charge fluctuation of a motorcycle engine under wide operating conditions were investigated by experiment. Several key engine operating parameters (engine speed/load, air/fuel ratio, compression ratio and ignition mode) were considered and analyzed thoroughly. A new concept of intake charge time-pressure value (TPV) was proposed to estimate its charge capacity, and its fluctuation’s contribution to CCV was also assessed. Some important findings include: 1) the CCV goes up with engine speed. Engine speed is also the most important factor to affect intake charge fluctuation, coefficient of variation (COV) of TPV is only 3.38% at 3000 rpm under 60% load, but it rises up to 13.41% at 5000 rpm; 2) the contribution of charge cyclic fluctuation to CCV decreases with engine speed. At 3000 rpm, over 80% of CCV are caused by TPV’s fluctuation for all engine loads, but its contribution drops to about 30% at 5000 rpm under medium to full load; 3) engine load has moderate impact on intake charge fluctuation’s contribution to engine CCV within test range. This depends on the competition between intake pressure loss and trapped ability of residual gas; 4) the three factors of air/fuel ratio, compression ratio and ignition mode do not affect much the air exchange process, but largely influence the combustion process. The more they improve combustion process, the larger degree of participation in engine CCV by intake charge fluctuation.

Analysis of PPCI mode and multi-objective comprehensive optimization for a dual-fuel engine

The aim of this research is to find a favorable combination of the complex control parameters of a diesel/natural gas dual-fuel engine, so that polluting emissions can meet regulatory requirements and achieve relatively low fuel consumption. This research covers the effects of control parameters on the performance and emissions of a dual-fuel engine for different combustion modes as well as discussions on the optimization of the entire operating conditions in the partial premixed compression combustion ignition (PPCI) mode combined with long short-term memory networks (LSTM) and non-dominated sorting genetic algorithms (NSGA-II). LSTM is used for the first time to establish a predictive regression model for the calibration parameters and output response of a dual-fuel engine, achieving the optimized mapping of input and output parameters. All of the optimization scenarios can achieve a trade-off between fuel consumption and emissions. The engine test results show that for the entire working conditions for the optimized dual-fuel engine, the nitrogen oxides (NOx) emissions are reduced by 77%, and the fuel consumption is roughly equal to that of the original diesel engine. The test results of the four condition test cycle of a marine engine for propulsion show that the NOx emissions of the optimized dual-fuel engine are reduced by 26.6% compared with the Tier-III legal requirements.

The experimental verification of the multi-fuel IC engine concept with the use of jet propellant-8 (JP-8) and its blends with pure rapeseed oil

The paper presents some research results to recognize the possibility of realization of the idea of a multi-fuel IC engine. Future construction is planned as a flexible solution for military or special purpose transport means and emergency power generation. The proposed engine would utilize compression ignition mode for combustion of high reactive fuels (JP-8, diesel oil, etc.) or spark ignition mode for gasoline or other low reactive fuels. Practical implementation of the idea requires that highly reactive fuels be burned efficiently at a low compression ratio suitable for both engine modes. For the test diesel oil, JP-8 and its blends with pure rapeseed oil were chosen as easily accessible fuels. The experiment was carried out on naturally aspirated and supercharged AVL research engine with a common rail system and compression ratio CR = 12. The elaborated, unified injection strategy that synchronized the main dose injection timing with the start of the second stage of homogeneous mixture combustion was checked in practice. The proposed injection strategy applied for CI engine with the low compression ratio enabled efficient combustion and comparable, relatively high engine performance for all tested fuels.

Ignition behavior and the onset of quasi-detonation in methane-oxygen using different end wall reflectors

The shock wave focusing technique is beneficial to the development of detonation-based engines, which can shorten the long run-up distance that is usually required for a detonation, reducing the weight of the detonation engine. In this work, we performed experiments using different end wall reflectors to facilitate the formation and intensity of the combustion wave in a stoichiometric methane-oxygen mixture diluted by argon. By changing shock wave intensity, the effects of the incident shock Mach number (Ma) on the ignition delay times in two reflectors are systematically investigated. The experimental results show that the conical reflector creates an abrupt pressure rise in the apex, resulting in a 64.5% rise in the acceleration of the reflected shock velocity compared with the planar reflector. The introduction of a conical reflector significantly shortens the ignition delay time by an order of magnitude and facilitates the amalgamation of the leading reflected shock wave and the subsequent combustion wave. The experimental results also illustrate that conical reflectors promote the formation of the second ignition. However, only a weak deflagration wave is formed in a planar reflector, and a strong deflagration wave and quasi-detonation wave are observed by using a conical reflector. Our observation sheds light on the mechanism of ignition modes induced by the shape of reflectors.

Effects of hydrogen flow rate, injection pressure and EGR on performance of common rail direct injection (CRDi) engine in dual fuel mode

PurposeThe different performance tests were conducted on diesel engine compression ignition (CI) mode and CRDi engine.Design/methodology/approachThe CI engine was suitably modified to CRDi engine with Toroidal re-entrant combustion chamber (TRCC) and was run in dual-fuel (DF) mode. Hydrogen (H2) was supplied at different flow rates during the suction stroke, and 0.22 Kg/h of hydrogen fuel flow rate (HFFR) was found to be optimum. Diesel and biodiesel were used as pilot fuels. The CRDi engine with DF mode was run at various injection pressures, and 900 bar was found to be optimum injection pressure (IP) with 10o before top dead center (bTDC) as fuel injection timing (IT).FindingsThese operating engine conditions increased formation of oxides of nitrogen (NOx), which were reduced by exhaust gas recycle (EGR). With EGR of 15%, CRDi engine resulted in 12.6% lower brake thermal efficiency (BTE), 5.5% lower hydrocarbon (HC), 7.7% lower carbon monoxide (CO), 26% lower NOx at 80% load as compared to the unmodified diesel engine (CI mode).Originality/valueThe current research is an effort to study and evaluate the performance of CRDi engine in DF mode with diesel-H2 and BCPO-H2 fuel combinations with TRCC.

Evaluation of reactivity controlled compression ignition mode combustion engine using mineral diesel/gasoline fuel pair

Stricter emission norms, scarce availability of conventional fuel resources, and moderate engine efficiency are primary concerns for both spark ignition (SI) and compression ignition (CI) engines. The use of advanced low-temperature combustion technologies can resolve these issues, amongst which reactivity-controlled compression ignition (RCCI) mode combustion has emerged as an important one. RCCI mode combustion exhibits significantly lower exhaust emissions (oxides of nitrogen [NOx] and particulate matter [PM]) compared to CI mode combustion and delivers higher BTE compared to SI mode combustion. In this study, RCCI mode combustion has been investigated in a single-cylinder research engine using gasoline and mineral diesel as low reactivity fuel (LRF) and high reactivity fuel (HRF), respectively. Experiments have been performed at different premixed ratios of LRF (premixed ratio [rp] = 0, 0.25, 0.50, and 0.75) and four-engine loads (1 bar to 4 bar BMEP) at a constant engine speed of 1500 rpm. The use of gasoline in RCCI mode combustion resulted in relatively smoother RCCI mode combustion compared to baseline CI mode combustion. The presence of low reactivity gasoline led to a slightly retarded start of combustion (SoC) and combustion phasing (CP), which improved the performance of the RCCI mode combustion engine. RCCI mode combustion produced relatively lower NOx emissions compared to baseline CI mode combustion. However, hydrocarbon (HC) and carbon monoxide (CO) emissions from RCCI mode combustion were significantly higher than the CI mode combustion. Lower PM emissions from RCCI mode combustion was an important observation of this investigation. Qualitative correlations between different parameters such as PM number and mass-size distributions, total particulate mass (TPM)-NOx, etc., revealed that RCCI mode combustion was capable of simultaneous reduction of NOx and PM, which is otherwise difficult in conventional CI mode combustion engines

Clean combustion and emissions strategy using reactivity controlled compression ignition (RCCI) mode engine powered with CNG-Karanja biodiesel

Heterogeneous combustion in a diesel engine is noisier, uncontrolled and more polluting. This can be achieved with a strategic approach of a reactivity-controlled compression ignition (RCCI) mode engine that operates with low and high reactive fuel combinations. In the present work, a diesel engine is operated in RCCI mode with gaseous fuels viz. CNG as a primary fuel and a blend of diesel and Karanja biodiesel (BD20) as pilot fuel. This research aims to determine the operating limits of CNG fuel for less noisy combustion and clean exhaust.Further, relative air-fuel ratio (λ), cycle to cycle variations, combustion noise and emissions were studied for full load operation. The CRDI engine is optimized for diesel operation with a split injection strategy. The knock limits for CNG as the primary fuel are obtained. The combustion noise increases at a higher energy share by CNG. Also, higher values of HC and CO emissions are observed. This may be due to higher energy share values, flame speed and octane number of CNG fuel.Further, NOx emissions and smoke are decreased. The CNG induction of 10 ms with 90% ES can be noted as a knock limit for 3.5 kW power. The highest BTHE of 24.2% and least BSFC 0.3 kg/kWhr reported by 60%ES of LRF is better than diesel and KBD20 fuel. An optimum 60% energy share of CNG is observed for clean combustion and emissions strategy using the RCCI mode of a modified diesel engine.

Statistical and experimental investigation of the influence of fuel injection strategies on CRDI engine assisted CNG dual fuel diesel engine

With an alarming enlargement in vehicular density, there is a threat to the environment due to toxic emissions and depleting fossil fuel reserves across the globe. This has led to the perpetual exploration of clean energy resources to establish sustainable transportation. Researchers are continuously looking for the fuels with clean emission without compromising much on vehicular performance characteristics which has already been set by efficient diesel engines. In this study, the combustion, performance and emission characteristics of CRDI diesel engine assisted CNG dual fuel research engine operated at constant speed of 1500 rpm with variable engine load (16, 20 and 24 NM) to analyses the influence of fuel injection timings (7.5, 12.5 and 17.5 SOI) and fuel injection pressure (500, 750 and 1000 bar) under reactivity-controlled compression ignition (RCCI) mode. In the case of a fuel injection pressure of 1000 bar, the maximum brake specific fuel consumption of 0.42 kg/kWh is registered with a brake mean effective pressure of 3.2 bar. Response surface methodology has been used in this analysis for predicting the optimal input parameters (engine load, fuel injection timing, and fuel injection pressure), which results in an optimal combination of performance (BP, BTHE, and BSFC) and emission (HC, NOx, and CO) parameters. A variety of optimal solutions based on the desirability method is obtained from the model, and optimal input parameters is suggested as load 20(Nm), injection pressure 750(Bar), and injection timing (BTDC) 12.5. Additionally, to obtain a ‘regression model’ a statistically significant test (ANOVA) is developed. Results have shown that the suggested ‘Regression Model’ is best fitted to 0.095 standard deviations, 0.972 corrected R2, and 18.482 acceptable accuracy.

Parametric investigation on hydrogen driven homogeneous charge compression ignition mode with advanced diesel injection using chemical kinetics based numerical model

In the present study, a numerical model based on chemical kinetics was developed to investigate the effect of different parameters on characteristics of hydrogen diesel homogeneous charge compression ignition (HDHCCI) mode. The results showed that the combustion process was retarded with diminished cool flame as increasing hydrogen energy share (HES) due to reduction of H2O2, H2O and OH radicals with hydrogen addition. Thus, it increased the indicated thermal efficiency (ITE) and decreased the indicated specific energy consumption (ISEC). The levels of NOx and soot emissions were reduced by 22% and 63% at maximum HES. A spray angle of 10° decreased the total fuel impingement compared with a spray angle of 74° because of improvement in air-fuel mixing phenomena. Incomplete combustion was recovered at HES of 25% when increasing the charge temperature or adapting the twin-pulse in HDHCCI mode, consequently the ITE was improved with a decrease in ISEC.

Model for Loading Characteristics of Gas Explosion in a Utility Tunnel

Gas safety in a utility tunnel is an important scientific problem. In this study, explosion model tests of methane–air mixed gas were conducted to evaluate the safety of the gas. Furthermore, the influences of the concentration of mixed air, ignition mode, and opening area on propagation and distribution law of the blast wave were investigated. The results demonstrated that a significant explosion phenomenon existed if the methane concentration reached 10.5%, manifested by the largest explosion overpressure peak and the highest overpressure growth rate. Flame propagation was accelerated after the explosion under chemical ignition. The overpressure peak was an average of approximately 70% higher than that under the electrode ignition. The explosion overpressure and its impulse can be reduced effectively only for a certain proportion of the tunnel opening area. Therefore, the present study can provide a comprehensive understanding of the loading characteristics and the corresponding mechanism for a gas explosion in various practical tunnels.

Fire boundaries of lithium-ion cell eruption gases caused by thermal runaway

SummaryLithium-ion batteries are applied in electric vehicles to mitigate climate change. However, their practical applications are impeded by poor safety performance owing mainly to the cell eruption gas (CEG) fire triangle. Here, we report quantitatively the three fire boundaries corresponding to the CEG fire triangle of four types of mainstream cells with the state of charge (SOC) values ranging from 0% to 143% based on 29 thermal runaway tests conducted in an inert atmosphere in open literature. Controlling the SOC and/or selecting a reasonable cell type can alter the minimum CEG and oxygen concentrations required for ignition, thereby changing the probability of a battery fire. The ignition temperature varies greatly according to the type of ignition source type. Temperature and ignition source type play a leading role in the ignition mode. Breaking any fire boundary will stop the ignition of CEG, thus significantly improving the battery safety performance.

Effect of wood structure geometry during firebrand generation in laboratory scale and semi-field experiments

As the set of experiments result, statistically substantiated data were obtained on the laws of ignition of a model angular structure under conditions of a point source of heat exposure. The use of IR diagnostics made it possible to control the thermal picture in the experimental area, as well as to capture areas of the highest and lowest heating. In the Large Aerosol Chamber of IAO SB RAS, preliminary experiments were carried out on a “firebrand shower” model exposure, which is naturally occurring firebrands (flaming or glowing embers) with some types of construction materials (chipboards). The exposure of the samples to firebrands stream was provided using a firebrand generator of own original design. It was experimentally confirmed that particle size plays a significant role in the ignition of a building structure. If the characteristic particle size, which can be defined as the ratio of its volume to the surface area in contact with the wood, is less than a certain characteristic value, then the ignition mode with a sharp temperature maximum near the phase interface is not fulfilled. This can be explained by the prevailing heat removal into the external environment in comparison with the amount of heat coming from a heat gun and resulting from chemical reactions.

Effect of cavity arrangement on the ignition mode of vaporized kerosene in supersonic flow

The ignition characteristics and flame stabilization of vaporized kerosene are experimentally investigated in a direct-connected model engine. The incoming flow of Ma 2.0 is generated by an air heater at a total pressure of 0.98 MPa and a stagnation temperature of 920 K, which simulates flight conditions at a height of 17 km and flow of Ma 4.0. Vaporized China RP-3 aviation kerosene is employed as fuel in a single-side expansion combustor. The result shows that the ignition characteristics are closely related to the cavity location and configuration. Four modes of ignition are classified in this paper, and an orthogonal distribution of the mode with the injection pressure and temperature variations is studied in detail. Ignition in the downstream single cavity is more difficult than that in the upstream cavity but more easily generates an intensive flame stabilized in the cavity shear layer. The existence of an ignition threshold is responsible for this difference. Only if the injection condition exceeds the critical point can the flame be established and directly reach an intensive state. In a tandem dual cavity, the ignition mode distribution is similar to that of a single cavity under lean fuel conditions. Without a shock train in the flow field, the coupling effect of the two cavities on the ignition mode transition is not obvious.

Numerical Analysis of Fuel Effects on Advanced Compression Ignition Using a Cooperative Fuel Research Engine Computational Fluid Dynamics Model

AbstractGrowing environmental concerns and demand for a better fuel economy are driving forces that motivate the research for more advanced engines. Multi-mode combustion strategies have gained attention for their potential to provide high thermal efficiency and low emissions for light-duty applications. These strategies target optimizing the engine performance by correlating different combustion modes to load operating conditions. The extension from boosted spark ignition (SI) mode at high loads to advanced compression ignition (ACI) mode at low loads can be achieved by increasing the compression ratio and utilizing intake air heating. Further, in order to enable an accurate control of intake charge condition for ACI mode and rapid mode-switches, it is essential to gain fundamental insights into the autoignition process. Within the scope of ACI, homogeneous charge compression ignition (HCCI) mode is of significant interest. It is known for its potential benefits, operation at low fuel consumption, low NOx, and particulate matter (PM) emissions. In the present work, a virtual Cooperative Fuel Research (CFR) engine model is used to analyze fuel effects on ACI combustion. In particular, the effect of fuel octane sensitivity (S) (at constant Research Octane Number (RON)) on autoignition propensity is assessed under beyond-RON (BRON) and beyond-MON (BMON) ACI conditions. The three-dimensional CFR engine computational fluid dynamics (CFD) model employs a finite-rate chemistry approach with a multi-zone binning strategy to capture autoignition. Two binary blends with Research Octane Number (RON) of 90 are chosen for this study: primary reference fuel (PRF) with S = 0 and toluene–heptane (TH) blend with S = 10.8, representing paraffinic and aromatic gasoline surrogates. Reduced mechanisms for these blends are generated from a detailed gasoline surrogate kinetic mechanism. Simulation results with the reduced mechanisms are validated against experimental data from an in-house CFR engine, with respect to in-cylinder pressure, heat release rate, and combustion phasing. Thereafter, the sensitivity of combustion behavior to ACI operating condition (BRON versus BMON), air-fuel ratio (λ = 2 and 3), and engine speed (600 and 900 rpm) is analyzed for both fuels. It is shown that the sensitivity of a fuel’s autoignition characteristics to λ and engine speed significantly differs at BRON and BMON conditions. Moreover, this sensitivity is found to vary among fuels, despite the same RON. It is also observed that the presence of low-temperature heat release (LTHR) under BRON condition leads to more sequential autoignition and longer combustion duration than BMON condition. Finally, the study indicates that the octane index (OI) fails to capture the trend in the variation of autoignition propensity with S under the BMON condition.

Low temperature autoignition of Jet A and surrogate jet fuel

An experimental study of the low-temperature and low-pressure autoignition of Jet A and surrogate fuels was conducted using the ASTM-E659 standardized test method. Two surrogate fuels (Aachen and JI mixtures), their individual components and two batches (POSF-4658 and POSF-10325) of standardized Jet A were tested using the ASTM-E659 method for a range of fuel concentrations and temperatures. The ignition behaviors were categorized into four distinct ignition modes. The individual hydrocarbon components had a wide range of ignition behaviors and minimum autoignition temperatures (AIT) values depending on the molecular structure. The two Jet A batches showed similar ignition behavior with measured AITs of 229 ±3°C and 225 ±3°C respectively. Both surrogates exhibited similar ignition behavior to Jet A with comparable AITs of 219 ±3.1°C (Aachen) and 228 ±3°C (JI) with the JI mixture proving to be a more suitable surrogate to Jet A in the low-temperature thermal ignition regime.

Experimental investigation on compression ignition engine powered with pentanol and thevetia peruviana methyl ester under reactivity controlled compression ignition mode of operation

In the current study, an effort is carried out to study the influence of pentanol as low reactive fuel (LRF) along with diesel and Thevetia peruviana methyl ester (TPME) as high reactive fuels (HRF) in reactivity controlled compression ignition (RCCI) engine. The experiments are conducted on dual fuel engine at 50% load for RCCI mode of operation by varying pentanol percentage in injected fuels. The results revealed that RCCI mode of operation at 10% of pentanol in injected fuels exhibited higher brake thermal efficiency (BTE) of 22.15% for diesel and pentanol fuel combination, which is about 9.1% and 27.3% higher than other B20 and pentanol, B100 and pentanol fuel combinations respectively. As the percentage of pentanol increased in injected fuels, hydrocarbon (HC) and carbon monoxide (CO) emissions are increased while nitrogen oxide (NOx) and smoke emissions are decreased. Among various fuel combinations tested diesel and pentanol fuel combination gives lower HC, CO and smoke emissions and higher NOx emissions. At 10% pentanol in injected fuels, the highest heat release rate (HRR) and in-cylinder pressure are found for diesel and pentanol fuel combinations compared with other fuels.

Effects of Two Pilot Injection on Combustion and Emissions in a PCCI Diesel Engine

The effects of two pilot injections on combustion and emissions were evaluated in a single−cylinder turbocharged diesel engine, which operated in premixed charge compression ignition (PCCI) modes with multiple injections and heavy exhaust gas recirculation under the low load by experiments and simulation. It was revealed that with the delay of the start of the first pilot injection (SOI−P1) or the advance of the start of second pilot injection (SOI−P2), respectively, the pressure, heat release rate (HRR), and temperature peak were all increased. Analysis of the combustion process indicates that, during the two pilot injection periods, the ignition timing was mainly determined by the SOI−P2 while the first released heat peak was influenced by SOI−P1. With the delay of SOI−P1 or the advance of SOI−P2, nitrogen oxide (NOx) generation increased significantly while soot generation varied a little. In addition, increasing Q1 and decreasing the second pilot injection quantity (Q2) can manipulate the NOx and soot at a low level. The advance in SOI−P2 of 5 °CA couple with increasing Q1 and reducing Q2 was proposed, which can mitigate the compromise between emissions and thermal efficiency under the low load in the present PCCI mode.