Guohong Tian

Investigation into Light Duty Dieseline Fuelled Partially-Premixed Compression Ignition Engine

Conventional diesel fuelled Partially-Premixed Compression Ignition (PPCI) engines have been investigated by many researchers previously. However, the ease of ignition and difficulty of vaporization of diesel fuel make it imperfect for PPCI combustion. In this study, Dieseline (blending of diesel and gasoline) was looked into as the Partially-Premixed Compression Ignition fuel for its combination of two fuel properties, ignition-delay-increasing characteristics and higher volatility, which make it more suitable for PPCI combustion compared to neat diesel. A series of tests were carried out on a Euro IV light-duty common-rail diesel engine, and different engine modes, from low speed/load to middle speed/load were all tested, under which fuel blend ratios, EGR rates, injection timings and quantities were varied. The emissions, fuel consumption and combustion stability of this dieseline-fuelled PPCI combustion were all investigated. The results showed that dieseline had great advantages as a PPCI combustion fuel in terms of emission reduction. This was particularly significant at high-speed engine mode. It was also found that with a blend of 50% gasoline in diesel, the particle numbers total concentration could be reduced by 90% while low NOx level and high brake fuel conversion efficiency (around 30%) were maintained at all the loads tested.

Study of the Effect of Spark Ignition on Gasoline HCCI Combustion

Abstract Homogeneous charge compression ignition (HCCI) has challenges with regard to ignition control. A spark-assisted gasoline HCCI combustion strategy was used to control ignition of HCCI combustion. In this paper, the effects of spark ignition (SI) on HCCI combustion were investigated on a gasoline direct injection (GDI) engine. The experimental results show that SI improves the stability of HCCI combustion at HCCI critical status (HCCI-CS). At the transition from SI to HCCI mode, the transition fluctuations can be smoothed by the SI in SI/HCCI hybrid combustion engine. Local SI can trigger entire HCCI in the cylinder at sub-HCCI-CS. Without SI, misfire occurs at sub-HCCI-CS. The reason is that local high temperature and pressure owing to local heat release from the spark electrode leads to increase of temperature and pressure in the entire cylinder. When the temperature and concentration of mixture are below sub-HCCI-CS, SI has little effect on HCCI ignition.

Spray Characteristics Study of DMF Using Phase Doppler Particle Analyzer

2,5-dimethylfuran (DMF) is currently regarded as a potential alternative fuel to gasoline due to the development of new production technology. In this paper, the spray characteristics of DMF and its blends with gasoline were studied from a high pressure direct injection gasoline injector using the shadowgraph and Phase Doppler Particle Analyzer (PDPA) techniques, This includes the spray penetration, droplet velocity and size distribution of the various mixtures. In parallel commercial gasoline and ethanol were measured in order to compare the characteristics of DMF. A total of 52 points were measured along the spray so that the experimental results could be used for subsequent numerical modeling. In summary, the experimental results showed that DMF and its blends have similar spray properties to gasoline, compared to ethanol. The droplet size of DMF is generally smaller than ethanol and decreases faster with the increase of injection pressure. The mean velocity of DMF spray droplets is similar to gasoline and higher than ethanol. Ultimately, the spray characteristics of DMF are better suited to the gasoline engine technology than its counterpart, ethanol.

Mode Switch of SI-HCCI Combustion on a GDI Engine

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. Copyright

Development Approach of a Spark-Ignited Free-Piston Engine Generator

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Effects of Combustion Phasing, Injection Timing, Relative Air-Fuel Ratio and Variable Valve Timing on SI Engine Performance and Emissions using 2,5-Dimethylfuran

Ethanol has long been regarded as the optimal gasoline-alternative biofuel for spark-ignition (SI) engines. It is used widely in Latin and North America and is increasingly accepted as an attractive option across Europe. Nevertheless, its low energy density requires a high rate of manufacture; in areas which are deficient of arable land, such rates might prove problematic. Therefore, fuels with higher calorific values, such as butanol or 2,5-dimethylfuran (DMF) deserve consideration; a similar yield to ethanol, in theory, would require much less land. This report addresses the suitability of DMF, to meet the needs as a biofuel substitute for gasoline in SI engines, using ethanol as the biofuel benchmark. Specific attention is given to the sensitivity of DMF to various engine control parameters: combustion phasing (ignition timing), injection timing, relative air-fuel ratio and valve timing (intake and exhaust). Focus is given to the window for optimization; the parameter range which sustains optimal IMEP (within 2%) but provides the largest reduction of emissions (HC or NOx). The test results using a single cylinder SI research engine at 1500rpm show how DMF is less sensitive to key engine parameters, compared to gasoline. This allows a wider window for emissions optimization because the IMEP remains optimal across a greater parameter range. Copyright

Control of a spark ignition homogeneous charge compression ignition mode transition on a gasoline direct injection engine

Abstract The hybrid combustion mode is an ideal operation strategy for a gasoline homogeneous charge compression ignition (HCCI) engine. A stable and smooth spark ignition (SI)/HCCI switch has been an issue in the research on multimode combustion. In this paper, the switch process has two key issues; the cam profile and throttle opening. With the developed two-stage cam system, the valve phase strategy can be switched within one engine cycle, from the normal cam profile for the SI mode to a negative valve overlap (NVO) profile for the HCCI mode, or vice versa. For a smoother and more stable switch, the throttle change was separated from the cam profile switch, which was called the stepped switch. The effect of throttle opening on HCCI combustion was studied, and the results showed that the concept of the stepped switch was reliable. With gasoline direct injection (GDI) the combustion mode switches from both SI and HCCI sides were smooth, rapid, and robust, without any abnormal combustion such as knocking and misfiring.

Experimental and computational studies on gasoline HCCI combustion control using injection strategies

Homogeneous Charge Compression Ignition (HCCI) has challenges of ignition control. In this paper, HCCI ignition timing and combustion rate were controlled by two-stage direct injection (TSDI) strategies on a four-stroke gasoline HCCI engine. TSDI strategy was proposed to solve the two major problems of HCCI application-ignition control and load extension. Both simulation and experiments were carried out on a gasoline HCCI engine with negative valve overlap (NVO). An engine model with detailed chemical kinetics was established to study the gas exchange process and the direct injection strategy in the gasoline HCCI engine with TSDI and NVO. Simulation results were compared with experiments and good agreement was achieved. The simulated and experimental results provided a detailed insight into the processes governing ignition in the HCCI engine. Using TSDI, the fuel concentration, temperature as well as chemical species can be controlled. The effects of different injection parameters, such as split injection ratio and start-of-injection (SOI) timing, were studied. The experimental results indicate that, two-stage direct injection is a practical technology to control the ignition timing and combustion rate effectively in four-stroke gasoline HCCI engines. Both the high load and low load limits of HCCI operation were extended.

DMF - A New Biofuel Candidate

This book aspires to be a comprehensive summary of current biofuels issues and thereby contribute to the understanding of this important topic. Readers will find themes including biofuels development efforts, their implications for the food industry, current and future biofuels crops, the successful Brazilian ethanol program, insights of the first, second, third and fourth biofuel generations, advanced biofuel production techniques, related waste treatment, emissions and environmental impacts, water consumption, produced allergens and toxins. Additionally, the biofuel policy discussion is expected to be continuing in the foreseeable future and the reading of the biofuels features dealt with in this book, are recommended for anyone interested in understanding this diverse and developing theme.

Split-Injection Strategies under Full-Load Using DMF, A New Biofuel Candidate, Compared to Ethanol in a GDI Engine

It is well known that direct-injection (DI) is a technology enabler for stratified combustion in spark-ignition (SI) engines. At full-load or wide-open throttle (WOT), partial charge stratification can suppress knock, enabling greater spark advance and increased torque. Such split-injection or double-pulse injection strategies are employed when using gasoline in DI (GDI). However, as the use of biofuels is set to increase, is this mode still beneficial? In the current study, the authors attempt to answer this question using two gasoline-alternative biofuels: firstly, ethanol; the widely used gasoline-alternative biofuel and secondly, 2,5-dimethylfuran (DMF); the new biofuel candidate. These results have been benchmarked against gasoline in a single-cylinder, spray-guided DISI research engine at WOT (λ=1 and 1500rpm). Firstly, single-pulse start of injection (SOI) timing sweeps were conducted with each fuel to find the highest volumetric efficiency and IMEP. The resulting optimum SOI timing for gasoline was then used as the first injection (SOI1) with each fuel in the split-injection tests. In this instance, second SOI timing (SOI2) sweeps were made using two split-ratios (SOI1:SOI2 = 1:1 and 2:1). For the single-pulse SOI timing sweeps, the change in IMEP when using ethanol is symmetrical either side of the maximum. However, when using gasoline and DMF, the behavior is asymmetrical, with maximums later and earlier than with ethanol, respectively. For split-injection, the maximum IMEP increases when fuelled with the biofuels, whilst maintaining acceptable engine stability. This increase, however, is much more dependent on SOI2 timing than with gasoline, due to the deterioration of in-cylinder mixing and slower combustion. Copyright