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To understand the mechanism of the combustion by torch flame jet in a gas engine with pre-chamber and also to obtain the strategy of improving thermal efficiency by optimizing the structure of pre-chamber including the diameter and number of orifices, the combustion process was investigated by three dimensional numerical simulations and experiments of a single cylinder natural gas engine. As a result, the configuration of orifices was found to affect the combustion performance strongly. With the same orifice diameter of 1.5mm, thermal efficiency with 7 orifices in pre-chamber was higher than that with 4 orifices in pre-chamber, mainly due to the reduction of heat loss by decreasing the impingement of torch flame on the cylinder linear. Better thermal efficiency was achieved in this case because the flame propagated area increases rapidly while the flame jets do not impinge on the cylinder wall intensively.

For passenger vehicles with direct injection (DI) diesel engines, it is desirable for the engine to have high speed and high power output performance comparable to that of gasoline engines, yet maintaining its good fuel economy. Accordingly, we examine a dual inlet port system, which operates both valves simultaneously at high engine speed to improve the volumetric efficiency but operates only one valve at low engine speed to obtain the optimum swirl ratio (SR). The swirl ratio with two valve operation (SR1+2) is affected by SR and the mean effective valve area (Zm) of each valve. Therefore, with experimental technique, it is difficult to find port configurations which are optimum for both high and low engine speeds simultaneously. We have employed a predictive method to obtain the optimum configurations. This paper describes how to derive the predictive equation of SR1+2 from the SR and Zm of each valve for the optimum intake system design.

This paper describes the evaluation of flow characteristics inside a model engine cylinder using particle image velocimetry (PIV), laser Doppler anemometry (LDA), and numerical simulation by Partial Cells in Cartesian coordinate (PCC) method. The main goal of the study is to clarify the differences in the velocity characteristics obtained by these methods. The model engine head has a four-valve system. Single- and dual- valve opening conditions of the model engine head were tested by a steady flow test rig. The flow structures were completely different for these valve opening conditions. The mean velocities and their distributions obtained by the three methods show satisfactory agreement. However, there were differences in the turbulence intensities under several conditions and measuring positions. Taylor's hypothesis in the integral length scale of turbulence was also compared with single LDA and PIV measurements.