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Technical Paper

Knocking Suppression using Stratified Stoichiometric Mixture in a DISI Engine

2010-04-12
2010-01-0597
Knocking is the main obstacle of increasing compression ratio to improve the thermal efficiency of gasoline engines. In this paper, the concept of stratified stoichiometric mixture (SSM) was proposed to suppress knocking in gasoline engines. The rich mixture near the spark plug increases the speed of the flame propagation and the lean mixture in the end gas suppresses the auto ignition. The overall air/fuel ratio keeps stoichiometric to solve the emission problem using three way catalysts (TWC). Moreover, both the rich zone and lean zone lead to soot free combustion due to homogeneous mixture. The effect on the knocking of homogeneous and stratified mixture was studied in a direct injection spark ignition (DISI) engine using numerical simulation and experimental investigation respectively.
Technical Paper

An Experimental Study Using Spark-Assisted Stratified Compression Ignition (SSCI) Hybrid Combustion Mode for Engine Particle Number (PN) Reduction in a High Compression Ratio Gasoline Engine

2016-04-05
2016-01-0758
Particle Number (PN) have already been a big issue for developing high efficiency internal combustion engines (ICEs). In this study, controlled spark-assisted stratified compression ignition (SSCI) with moderate end-gas auto-ignition was used for reducing PN in a high compression ratio gasoline direct injection (GDI) engine. Under wide open throttle (WOT) and Maximum Brake Torque timing (MBT) condition, high external cooled exhaust gas recirculation (EGR) was filled in the cylinder, while two-stage direct injection was used to form desired stoichiometric but stratified mixture. SSCI combustion mode exhibits two-stage heat release, where the first stage is associated with flame propagation induced by spark ignition and the second stage is the result of moderate end-gas auto-ignition without pressure oscillation at the middle or late stage of the combustion process.
Technical Paper

Investigation on Ignition of a Single Lubricating Oil Droplet in Premixed Combustible Mixture at Engine-Relevant Conditions

2019-04-02
2019-01-0298
The ignition of lubricating oil droplet has been proved to be the main factor for pre-ignition and the following super-knock in turbocharged gasoline direct injection engine. In this paper, the ignition process of lubricating oil droplet in combustible ambient gaseous mixture was investigated in a rapid compression machine (RCM). The pre-ignition induction by oil droplet of the ambient gaseous mixture was analyzed under different initial droplet volume and effective temperature conditions. The oil droplet was suspended on a tungsten fiber in the combustion chamber and the ignition process was recorded by a high-speed camera through the quartz window mounted at the end of the combustion chamber. The pressure traces were also obtained by a sensor in order to get the ignition delay and analyze the combustion process in detail.
Technical Paper

Experimental Study of Lean Mixture Combustion at Ultra-High Compression Ratios in a Rapid Compression Machine

2018-04-03
2018-01-1422
In order to meet increasingly stringent fuel consumption and emission regulations, more attentions are paid to improve engine efficiency. A large amount of energy-saving technologies have been applied in automotive field especially in gasoline engines. It is well known that lean burn and ultra-high compression ratio technologies are two basic and important methods to increase efficiency. In this paper, a rapid compression machine was employed to study combustion process of lean iso-octane mixture at ultra-high compression ratios (16 to 19:1). Regardless of flammability of the mixture, spark was triggered at the timing right after the end of compression, then, the flame propagation and/or auto-ignition can be recorded using high-speed photography simultaneously. The effects of equivalence ratio (φ), compression ratio (ε), dilution ratio, and effective temperature (Teff) on the combustion process was investigated.
Technical Paper

Combustion and Emission Characteristics of Polyoxymethylene Dimethyl Ethers (PODE)/ Wide Distillation Fuel (WDF) Blends in Diesel Engine

2018-04-03
2018-01-0926
Wide Distillation Fuel (WDF), with a distillation range from Initial Boiling Point of gasoline to Final Boiling Point of diesel, can be easily gained directly by blending diesel with gasoline. However, the reduced auto-ignitability of WDF could lead to higher HC emissions. Polyoxymethylene Dimethyl Ethers (PODE), with good volatility and oxygen content of up to 49%, have great potential to improve combustion and emission characteristics, especially for soot reduction. Experiments were carried out in a light-duty four-cylinder diesel engine fueled with neat diesel, gasoline/diesel blends (GD), GD/PODE blends (GDP) and the combustion and emission characteristics were carefully examined. Results showed that GDP had the lowest PM emission and diesel had the poorest one among the three fuels. Due to the addition of gasoline and the relatively poor ignitability, GD had lower combustion efficiency and higher Soluble Organic Fraction (SOF) emissions than diesel.
Technical Paper

Effect of Thermodynamic Conditions on Spark Ignition to Compression Ignition in Ultra-Lean Mixture Using Rapid Compression Machine

2019-04-02
2019-01-0963
Compression ratio and specific heat ratio are two dominant factors influencing engine thermal efficiency. Therefore, ultra-lean burn may be one method to deal with increasingly stringent fuel consumption and emission regulations in the approaching future. To achieve high efficiency and clean combustion, innovative combustion modes have been applied on research engines including homogeneous charge compression ignition (HCCI), spark-assisted compression ignition (SACI), and gasoline direct-injection compression ignition (GDCI), etc. Compared to HCCI, SACI can extend the load range and more easily control combustion phase while it is constrained by the limit of flame propagation. For SACI with ultra-lean burn in engines, equivalence ratio (φ), rich-fuel mixture around spark plug, and supercharging are three essentials for combustion stability.
Technical Paper

Mode Switch of SI-HCCI Combustion on a GDI Engine

2007-04-16
2007-01-0195
Multi-mode combustion is an ideal combustion strategy to utilize HCCI for internal combustion engines. It combines HCCI combustion mode for low-middle load and traditional SI mode for high load and high speed. By changing the cam profiles from normal overlap for SI mode to the negative valve overlap (NVO) for HCCI mode, as well as the adjustment of direct injection strategy, the combustion mode transition between SI and HCCI was realized in one engine cycle. By two-step cam switch, the throttle action is separated from the cam action, which ensures the stabilization of mode transition. For validating the feasibility of the stepped switch, the influence of throttle position on HCCI combustion was carefully studied. Based on the research, the combustion mode switch was realized in one engine cycle; the whole switch process including throttle action was realized in 10 cycles. The entire process was smooth, rapid and reliable without any abnormal combustion such as knocking and misfiring.
Technical Paper

Modeling of HCCI Combustion: From 0D to 3D

2006-04-03
2006-01-1364
The detailed chemical kinetics was implemented into the 0D single-zone model, 1D engine cycle model and 3D CFD model respectively. Both simulation and experiment were carried out on a four-stroke gasoline HCCI engine with direct injection. The 0D model (HRG) was developed to study the isolating effect of HCCI parameters. The 1D engine cycle model with HRG was established to study the gas exchange process and the direct injection strategy in the gasoline HCCI engine with two-stage direct injection (TSDI) and negative valve overlap (NVO). The 3D model with HRG was constructed to study the ignition control mechanism in “two-zone HCCI” combustion via analysis the auto-ignition spots distribution in combustion chamber. “Two-zone HCCI” is defined in this paper as premixed ultra-lean compression ignition combining with premixed ultra-rich compression ignition. The three models were validated by experiments.
Technical Paper

Research on Steady and Transient Performance of an HCCI Engine with Gasoline Direct Injection

2008-06-23
2008-01-1723
In this paper, a hybrid combustion mode in four-stroke gasoline direct injection engines was studied. Switching cam profiles and injection strategies simultaneously was adopted to obtain a rapid and smooth switch between SI mode and HCCI mode. Based on the continuous pressure traces and corresponding emissions, HCCI steady operation, HCCI transient process (combustion phase adjustment, SI-HCCI, HCCI-SI, HCCI cold start) were studied. In HCCI mode, HCCI combustion phase can be adjusted rapidly by changing the split injection ratio. The HCCI control strategies had been demonstrated in a Chery GDI2.0 engine. The HCCI engine simulation results show that, oxygen and active radicals are stored due to negative valve overlap and split fuel injection under learn burn condition. This reduces the HCCI sensitivity on inlet boundary conditions, such as intake charge and intake temperature. The engine can be run from 1500rpm to 4000rpm in HCCI mode without spark ignition.
Technical Paper

Multi-dimensional Simulation of HCCI Engine Using Parallel Computation and Chemical Kinetics

2008-04-14
2008-01-0966
This study improved the computational efficiency significantly using parallel computation and reduced mechanisms. A 3-dimensional engine moving mesh of intake port, exhaust port and combustion chamber was established for HCCI engine cycle simulation. To achieve a more accurate analysis, chemical kinetics was implemented into the CFD code to study the intake, spray, ignition, combustion, and pollution formation process in HCCI engine. The simulations were run on a cluster of 16-CPU, parallelized by Message-Passing Interface (MPI) mode. The cases with detailed and reduced reaction mechanisms were calculated using 1, 2, 4, 8, 16 CPUs respectively and the corresponding computational time and speed-up were discussed. Using MPI 8-CPU with reduced mechanism (less than 40 species) is the optimal scheme for CFD/Chemistry calculation of typical HCCI engine.
Technical Paper

Effects of Temporal and Spatial Distributions of Ignition and Combustion on Thermal Efficiency and Combustion Noise in DICI Engine

2014-04-01
2014-01-1248
The effects of the temporal and spatial distributions of ignition timings of combustion zones on combustion noise in a Direct Injection Compression Ignition (DICI) engine were studied using experimental tests and numerical simulations. The experiments were performed with different fuel injection strategies on a heavy-duty diesel engine. Cylinder pressure was measured with the sampling intervals of 0.1°CA in order to resolve noise components. The simulations were performed using the KIVA-3V code with detailed chemistry to analyze the in-cylinder ignition and combustion processes. The experimental results show that optimal sequential ignition and spatial distribution of combustion zones can be realized by adopting a two-stage injection strategy in which the proportion of the pilot injection fuel and the timings of the injections can be used to control the combustion process, thus resulting in simultaneously higher thermal efficiency and lower noise emissions.
Technical Paper

Combustion Mode Switch by Integrating Stoichiometric ASSCI Mode in a Four-cylinder Gasoline SI/HCCI Engine

2014-04-01
2014-01-1288
Homogeneous Charge Compression Ignition (HCCI) and Spark Ignition (SI) dual-mode operation provides a practical solution to apply HCCI combustion in gasoline engines. However, the different requirements of air-fuel ratio and EGR ratio between HCCI combustion and SI combustion results in enormous control challenges in HCCI/SI mode switch. In this paper, HCCI combustion was achieved in a four-cylinder gasoline direct injection engine without knock and misfire using close-loop control by knock index. Assisted Spark Stratified Compression Ignition (ASSCI) combustion was obtained stably at medium-high load. ASSCI combustion exhibits two-stage heat release with initial flame propagation and controlled auto-ignition. The knock index of ASSCI combustion is less than HCCI combustion due to the lower pressure rise rate.
Technical Paper

Investigations into Multiple Premixed Compression Ignition Mode Fuelled with Different Mixtures of Gasoline and Diesel

2015-04-14
2015-01-0833
A study of Multiple Premixed Compression Ignition (MPCI) with mixtures of gasoline and diesel is performed on a light-duty single cylinder diesel engine. The engine is operated at a speed of 1600rpm with the same fuel mass per cycle. By keeping the same intake pressure and EGR ratio, the influence of different blending ratios in gasoline and diesel mixtures (90vol%, 80vol% and 70vol% gasoline) is investigated. Combustion and emission characteristics are compared by sweeping the first (−95 ∼ −35deg ATDC) and the second injection timing (−1 ∼ 9deg ATDC) with an injection split ratio of 80/20 and an injection pressure of 80MPa. The results show that compared with diesel combustion, the gasoline and diesel mixtures can reduce NOx and soot emissions simultaneously while maintaining or achieving even higher indicated thermal efficiency, but the HC and CO emissions are high for the mixtures.
Technical Paper

An Experimental Study on the Effects of Split Injection in Stoichiometric Dual-Fuel Compression Ignition (SDCI) Combustion

2015-04-14
2015-01-0847
Stoichiometric dual-fuel compression ignition (SDCI) combustion has superior potential in both emission control and thermal efficiency. Split injection of diesel reportedly shows superiority in optimizing combustion phase control and increasing flexibility in fuel selection. This study focuses on split injection strategies in SDCI mode. The effects of main injection timing and pilot-to-total ratio are examined. Combustion phasing is found to be retarded in split injection when overmixing occurs as a result of early main injection timing. Furthermore, an optimised split injection timing can avoid extremely high pressure rise rate without great loss in indicated thermal efficiency while maintaining soot emission at an acceptable level. A higher pilot-to-total ratio always results in lower soot emission, higher combustion efficiency, and relatively superior ITE, but improvements are not significant with increased pilot-to-total ratio up to approximately 0.65.
Technical Paper

Numerical Simulation of HCCI Engine With Multi-Stage Gasoline Direct Injection Using 3D-CFD With Detailed Chemistry

2004-03-08
2004-01-0563
In this paper, the detailed chemical kinetics was implemented into the three-dimensional CFD code to study the combustion process in HCCI engines. An extended hydrocarbon oxidation reaction mechanism (89 species, 413 reactions) used for high octane fuel was constructed and then used to simulate the chemical process of the ignition, combustion and pollutant formation in HCCI conditions. The three-dimensional CFD / chemistry model (FIRE/CHEMKIN) was validated using the experimental data from a Rapid Compression Machine. The simulation results show good agreements with experiments. Finally, the improved multi-dimensional CFD code has been employed to simulate the intake, spray, combustion and pollution formation process of the gasoline direct injection HCCI engine with multi-stage injection strategy. The models account for intake flow structure, spray atomization, spray/wall interaction, droplet evaporation and gas phase chemistry in complex multi-dimensional geometries.
Technical Paper

Effects of Spark Ignition and Stratified Charge on Gasoline HCCI Combustion With Direct Injection

2005-04-11
2005-01-0137
HCCI combustion was studied in a 4-stroke gasoline engine with a direct injection system. The electronically controlled two-stage gasoline injection and spark ignition system were adopted to control the mixture formation, ignition timing and combustion rate in HCCI engine. The engine could be operated in HCCI combustion mode in a range of load from 1 to 5 bar IMEP and operated in SI combustion mode up to load of 8 bar IMEP. The HCCI combustion characteristics were investigated under different A/F ratios, engine speeds, starts of injection, as well as spark ignition enabled or not. The test results reveal the HCCI combustion features as a high-pressure gradient after ignition and has advantages in high thermal efficiency and low NOx emissions over SI combustion. At the part load of 1400rpm and IMEP of 3.5bar, ISFC in HCCI mode is 25% lower and NOx emissions is 95% lower than that in SI mode.
Technical Paper

Investigation into the Effect of Flame Propagation in the Gasoline Compression Ignition by Coupling G-Equation and Reduced Chemical Kinetics Combustion Model

2015-09-01
2015-01-1799
Gasoline Compression Ignition has been widely studied in recent years. The in-cylinder stratified charge in gasoline Partially Premixed Compression Ignition (PPCI) can extend the high load range with lower pressure rise rate than Homogeneous Charge Compression Ignition (HCCI). However, it is still not clear that whether there is flame propagation in the gasoline compression igntion mode and how the flame propagation influences the combustion process and pollution formation. In order to investigate the effect of flame, several gasoline compression ignition cases, including the single-stage and two-stage heat release processes, are simulated with the KIVA-3V Release 2 code in this study. The G-equation is employed to account for flame propagation, and the reduced i-octane/n-heptane mechanism is used to handle the chemical reactions. The results show that the flame propagation exists in the combustion process and it can accelerate the heat release slightly.
Journal Article

Experimental Investigation of Homogeneous Charge Induced Ignition (HCII) with Low-Pressure Injection to Reduce PM Emissions in a Heavy-Duty Engine

2016-04-05
2016-01-0775
Homogeneous Charge Induced Ignition (HCII) combustion utilizes a port injection of high-volatile fuel to form a homogeneous charge and a direct injection of high ignitable fuel near the Top Dead Center (TDC) to trigger combustion. Compared to Conventional Diesel Combustion (CDC) with high injection pressures, HCII has the potential to achieve diesel-like thermal efficiency with significant reductions in NOx and PM emissions with relatively low-pressure injections, which would benefit the engine cost saving remarkably. In the first part of current investigation, experiments were conducted at medium load with single diesel injection strategy. HCII exhibited great potential of using low injection pressures to achieve low soot emissions. But the engine load for HCII was limited by high heat release rate. Thus, in the second and third part, experiments were performed at high and low load with double diesel injection strategy.
Journal Article

Highly Turbocharged Gasoline Engine and Rapid Compression Machine Studies of Super-Knock

2016-04-05
2016-01-0686
Super-knock has been a significant obstacle for the development of highly turbocharged (downsized) gasoline engines with spark ignition, due to the catastrophic damage super-knock can cause to the engine. According to previous research by the authors, one combustion process leading to super-knock may be described as hot-spot induced pre-ignition followed by deflagration which can induce detonation from another hot spot followed by high pressure oscillation. The sources of the hot spots which lead to pre-ignition (including oil films, deposits, gas-dynamics, etc.) may occur sporadically, which leads to super-knock occurring randomly at practical engine operating conditions. In this study, a spark plasma was used to induce preignition and the correlation between super-knock combustion and the thermodynamic state of the reactant mixture was investigated in a four-cylinder production gasoline engine.
Journal Article

Performance, Combustion and Emission Characteristics of Polyoxymethylene Dimethyl Ethers (PODE3-4)/ Wide Distillation Fuel (WDF) Blends in Premixed Low Temperature Combustion (LTC)

2015-04-14
2015-01-0810
Wide Distillation Fuel (WDF) refers to the fuels with a distillation range from Initial Boiling Point (IBP) of gasoline to Final Boiling Point (FBP) of diesel. Polyoxymethylene Dimethyl Ethers (PODEn) have high oxygen content and cetane number, are promising green additive to diesel fuel. In this paper, WDF was prepared by blending diesel and gasoline at ratio of 1:1, by volume; the mass distribution of oligomers in the PODE3-4 product was 88.9% of PODE3 and 8.46% of PODE4. Diesel fuel (Diesel), WDF (G50D50) and WDF (80%)-PODE3-4 (20%) (G40D40P20) were tested in a light-duty single-cylinder diesel engine, combustion characteristic, fuel consumption and exhaust emissions were measured. The results showed that: at idling condition, G40D40P20 has better combustion stability, higher heat release rate, higher thermal efficiency compared with G50D50.
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