Tom Ma

Performance and Analysis of a 4-Stroke Multi-cylinder Gasoline Engine with CAI Combustion

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Innovative Ultra-low NOx Controlled Auto-Ignition Combustion Process for Gasoline Engines: the 4-SPACE Project

The purpose of the 4-SPACE (4-Stroke Powered gasoline Auto-ignition Controlled combustion Engine) industrial research project is to research and develop an innovative controlled auto-ignition combustion process for lean burn automotive gasoline 4-stroke engines application. The engine concepts to be developed could have the potential to replace the existing stoichiometric / 3-way catalyst automotive spark ignition 4-stroke engines by offering the potential to meet the most stringent EURO 4 emissions limits in the year 2005 without requiring DeNOx catalyst technology. A reduction of fuel consumption and therefore of corresponding CO2 emissions of 15 to 20% in average urban conditions of use, is expected for the « 4-SPACE » lean burn 4-stroke engine with additional reduction of CO emissions. This paper describes the first set of results of different experimental and numerical studies aiming to get such new combustion process in 4-stroke engines within the framework of this European consortium. One of the target of this consortium driven by IFP, is to develop a 4-stroke gasoline engine running conventionally at high load (with a normal compression ratio and without any intake air heating) and able to achieve Controlled Auto-Ignition (CAI) process at part load by reproducing the 2-stroke internal conditions (internal EGR rate and fluid dynamic control, temperature level...) favorable to this particular combustion process. For this purpose and as a starting point of the work program, a production 2-stroke engine known for its part load auto-ignition behavior is fully studied. Such work is focused on the analysis of in-cylinder conditions prior to auto-ignition using combined experimental testing, 3D CFD computations and optical diagnostics. From this analysis, 1D CFD computations have been extensively performed to evaluate the possible 4-stroke concepts able to reproduce internal conditions favorable to CAI. Then, the most “promising” configurations have been experimentally investigated. Encouraging preliminary results have already shown that NOx emissions are reduced by 10 to 40 times and the fuel economy is improved by 8 to 10% when compared with stoichiometric reference conditions. Other ways of getting auto-ignition of the lean fresh mixture are also explored by the project partners. The effects of several parameters, such as the fuel composition, the engine compression ratio, the intake air temperature level, etc... are also included in the research program. Thus, to analyze better analyze intrinsic autoignition process, specific tools as for example Rapid Compression Machine have been developed. Different fuels at various initial conditions (e.g. temperature, excess air) have been tested and compared, for example in terms for example of combustion rate and auto-ignition delay. Results obtained contribute to the better understanding of the auto-ignition process. Preliminary visualization results from specially designed single cylinder engines (2-stroke and 4-stroke) have been obtained for controlled auto-ignition combustion. The effect of charge stratification is briefly discussed.

Research and Development of Controlled Auto-Ignition (CAI) Combustion in a 4-Stroke Multi-Cylinder Gasoline Engine

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Experimental Studies on Controlled Auto-ignition (CAI) Combustion of Gasoline in a 4-Stroke Engine

This paper presents results from an experimental programme researching the in-cylinder conditions necessary to obtain gasoline Controlled Auto-ignition (CAI) combustion in a 4-stroke engine. A single-cylinder, variable compression ratio research engine is used for all experiments. Investigations concentrate on establishing the CAI operating range with regard to Air/Fuel ratio and Exhaust Gas Re-circulation (EGR) and their effect on ignition timing, combustion rate and variability, ISFC, and engine-out emissions, such as NOx, CO, and unburned HC. Comprehensive maps for each of the measured variables are presented and in relevant cases, these results are compared to those obtained during normal spark-ignition operation so that the benefits of CAI combustion can be more fully appreciated. Copyright

Dilution Effects on the Controlled Auto-Ignition (CAI) Combustion of Hydrocarbon and Alcohol Fuels

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Effect of Variable Engine Valve Timing on Fuel Economy

Variable Valve Timing (VVT) has been demonstrated by other authors as a means of improving engine performance and idle quality. The possibility of improving fuel economy as well with VVT is investigated here. Among these, Late Intake Valve Closing (LIVC) is shown to be practical concept applicable to engines with two intake valves per cylinder where the intake valves can be phased relative to each other to extend the total intake opening period

The exploitation of neural networks in automotive engine management systems

Abstract The use of electronic engine control systems on spark ignition engines has enabled a high degree of performance optimisation to be achieved. The range of functions performed by these systems, and the level of performance demanded, is rising and thus so are development times and costs. Neural networks have attracted attention as having the potential to simplify software development and improve the performance of this software. The scope and nature of possible applications is described. In particular, the pattern recognition and classification abilities of networks are applied to crankshaft speed fluctuation data for engine-fault diagnosis, and multidimensional mapping capabilities are investigated as an alternative to large ‘lookup’ tables and calibration functions.

CHARACTERISTICS OF HOMOGENEOUS CHARGE COMPRESSION IGNITION (HCCI) COMBUSTION AND EMISSIONS OF n-HEPTANE

ABSTRACT This paper reports the outcome from a systematic investigation carried out on HCCI (Homogeneous Charge Compression Ignition) combustion of a diesel type fuel. The n-heptane was chosen in this study to study the HCCI combustion characteristics of diesel engines with premixed charge by port fuel injection. Measurements were carried out in a single-cylinder, 4-stroke and variable compression ratio engine. Premixed n-heptane/air/EGR mixture was introduced into the cylinder by a port fuel injector and an external EGR system. The operating regions with regard to Air/Fuel ratio (A/F) and EGR rate were established for different compression ratios and intake temperatures. The effects of compression ratios, intake temperatures, A/F and EGR rates on knock limit, auto-ignition timing, combustion rate, IMEP and engine-out emissions, such as NOx, CO, and unburned HC, were analysed. The results have shown HCCI combustion of n-heptane could be implemented without intake charge heating with a typical diesel engine compression ratio. The attainable HCCI operating region was mainly limited by the knock limit, misfire, and low IMEP respectively. Higher intake temperature or compression ratio could extend the misfire limit of the HCCI operation at low load area but they would reduce the maximum IMEP limit at higher load conditions. Compared with conventional diesel combustion, HCCI combustion with diesel type fuels would lead to extremely low NOx emissions (less than 5 ppm) and smoke free exhaust, but would produce higher HC and CO emissions. An increase in intake temperature or compression ratio helped to reduce HC and CO emissions.

Characterization of an in-cylinder flow structure in a high-tumble spark ignition engine

Abstract A strong in-cylinder tumbling flow, which was produced by partially shrouding the lower periphery of the inlet valves, was measured in a three-valve twin-spark spark ignition (SI) engine using digital particle image velocimetry (PIV). Characteristics of the bulk flow, cyclic variation, frequency spectrum of velocity fluctuation, large- and small-scale fluctuation kinetic energy and integral length scale are analysed in detail. The possible effects of these flow characteristics on the charge stratification and subsequent ignition and combustion processes are also discussed. The results have shown that the strong tumble field was characterized by a very small velocity component in the direction of the tumble rotational axis until the late stage of the compression stroke. The cyclic variation of the bulk flow, though still present, was significantly reduced. Towards the end of the compression process, both low- and high-frequency velocity fluctuations were found to be high after the tumble had collapsed. The velocity fluctuation component along the cylinder axis was characterized by higher frequencies. An integral length scale was found in the range of 4–9 mm during the compression stroke.

The variation of in-Cylinder Mixture Ratios during Engine Cranking at Low Ambient Temperatures:

The development of mixture conditions in the cylinder of a fuel-injected spark ignition engine during engine cranking has been investigated at ambient temperatures down to —20°C. Mixtures near to the spark plug location were sampled and analysed to determine the air-fuel ratio and the relative proportions of light, medium and heavy components in the fuel. At low temperatures, the local air-fuel ratio varies substantially during the compression stroke, as does mixture composition. The change in mixture ratio over successive cycles of cranking depends on the fuel injected per cycle and the fuel-transfer characteristics of the intake port. The success or failure of combustion initiation is observed to depend only on the mixture air-fuel ratio at the spark plug. The upper limit on this mixture ratio for successful first-fire appears to be near to 35 : 1 by mass. Air-borne fuel in the cylinder accounts for only a small percentage of that supplied by the injector.