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A simplified turbulence model for predicating the in-cylinder turbulence parameters during combustion in a spark-ignition engine is investigated in this study. It is based on the standard k - ε model with the assumptions that no influence of squish and swirl is considered and that turbulence is in equilibrium. Hence it has a simplified form that meets the requirements for a two-zone quasi-dimensional combustion model. The proposed sub-model is implemented in a quasi-dimensional entrainment combustion model for spark-ignition engines. With this combustion model as the core system, a complete thermodynamics simulation system for a turbo-charged spark-ignition engine is programmed to simulate the working process and engine performance characteristics.

This paper investigates the effects of the variations of turbulence characteristics and initial flame kernel center position on the cyclic combustion variations by means of quasi-dimensional turbulent entrainment combustion model. The turbulence intensity and turbulence integral length scale at spark ignition time in the model are determined by maximizing the agreement between the predicted and measured results such as pressure diagrams, mass fraction burned etc. With different values of the turbulence intensity and turbulence integral length scale at spark ignition time, the calculation of the cyclic combustion variations for the engine is carried out. In addition, the prediction of the effect of different flame kernel center positions on the cyclic combustion variations is also studied. Finally, some conclusions are drawn out about the importance of turbulence and initial flame kernel center position on the cyclic combustion variations for spark-ignition engine.

A simple diaphragm injection carburettor (DIC) is developed and patented by the author in the paper. The principle is that, as the function of the diaphragm mechanism, the pressure difference between two sides of the metering hole equals the vacuum of the Venturi, so it can realize the pressurized fuel metering, by the fuel metering hole and vacuum from the Venturi, and fuel injection. The fuel is injected into the feed port and mixes with the small fraction of air through the port, the main port of fresh air from the crankcase is injected to the cylinder with the scavenging organized so that a separating layer is created between the exhaust and feed port, it can substantially reduce short-circuit. According to the characteristics of low short-circuit at low delivery ratio, the low load fuel supply system of conventional carburettor is preserved and combined with DIC which functions at high load operation.

Proper fuel supply system is the crux to realize the stratified scavenging for small type of two-stroke gasoline engine. A simple and effective diaphragm fuel injection system (DFI) is developed in the paper, which mainly consists of diaphragm pump and injector, the DFI utilizes the crankcase pressure which reflects the inlet flow rate to meter and inject fuel. As low short-circuit at low load operation, stratified scavenging seems not necessary, so the conventional carburetor is preserved to function at low load. This makes the whole fuel system simple and effective. The paper describes the operation principle of the DFI, and results of test on a 30cm3 modified engine are also presented, including the performance of fuel supply and contrast of complex engine performance with the original carbureted engine.

Heat transfer losses in the swirl chamber, throttling losses at the connecting passage and combustion delay in the main chamber are considered as the three factors influencing the thermal efficiency of IDI diesel engines. This paper suggests a thermodynamic model, in which three idealized diesel engines including no passage throttling engine, adiabatic diesel engine for swirl chamber and DI diesel engine are assumed, to isolate heat transfer losses, throttling losses and combustion delay in IDI diesel engines. The Second Law analysis is carried out by the thermodynamic state parameters calculated by the cycle simulation of engines based on the First Law. The effects of heat transfer losses in the swirl chamber, throttling losses at the connecting passage and combustion delay in the main chamber on the irreversibilities and availability losses during the engine cycle are analysed in detail. The relative influences among the three losses are also investigated.

The configuration of intake and exhaust manifolds has a strong impact on the gas exchange process of reciprocating engines. To make the designer assess a large number of manifold configurations quickly, a frequency analysis technique is developed, which is based on one-dimensional wave action equations. The frequency spectra of gas pressure pulsation in manifolds with different cylinder number, different manifold layouts and different manifold parameters are calculated, and the effects of various parameters on the spectrum characteristics are studied. The relationship between predicted frequency spectrum and measured volumetric efficiency is investigated for engines with different cylinder number. The experimental results for engines with different cylinder number show that this technique can be used to select the manifold parameters required in the initial stage of design and can save much CPU time compared to a siumlation program based on the method of characteristics.

A turbulent entrainment combustion model is considered to be reasonable for the combustion in spark-ignition engines. It is important to study the validation of this model for different combustion chamber shapes of the engines under various operating conditions. Nevertheless, the verification of this model has not been performed sufficiently. Based on some investigators' work of the turbulent eddy structure and turbulent characteristics in the cylinder of spark- ignition engine, a turbulent entrainment combustion model for spark- ignition engines is developed, and numerical simulation of combustion process is carried out in this study. The model is examined under various operating conditions of engine speed, loads, air- fuel ratio and spark timing for three shapes of combustion chambers: HRCC in head (compression ratio is 10), May process (compression ratio is 10 and 12 respectively) and Bowl- in- piston (compression ratio is 10).

This paper studied the flame initiation and early development in a spark ignition engine by using the Schlieren technique and a high speed camera. Some effects of different engine operating conditions and different spark energy are discussed. It was discovered that at any engine operating condition there exists a minimum flame propagation velocity during the early stage, and that its value as well as the corresponding time and flame radius can be used as a criterion to determine whether the early flame propagation is easy or not. To study the effects of different spark energy a special spark ignition system was designed which was controlled by a microcomputer for producing different spark energy levels. Both experimental and theoretical results show that the augmentation of breakdown energy in spark duration makes the original flame size increase effectively, which results in speeding up the flame kernel formation and early development.