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Instantaneous temperature of in-cylinder gas provides a lot of useful and local information for analyzing the combustion process in an internal combustion engine, so many optical pyrometries have been proposed and developed. Among others, the infrared monochromatic radiation pyrometry is considered to be more applicable to a practical engine due to requirement of only a single optical window, whereas two optical windows are indispensable for the conventional infrared absorption pyrometry. In this paper, the former pyrometer is used to measure the mean gas temperatures averaged on an optical path (or cylinder diameter) of a spark ignition engine, of which a prechamber is connected to the main chamber by a torch nozzle of various area sizes.

Two-dimensional combustion processes in a spark ignition engine with and without an unscavenged horizontal prechamber are calculated numerically using a k-e turbulence model, a flame kernel ignition model and an irreversible reaction model to obtain a better understanding of the spatial and temporal distributions of flow and combustion. The simulation results are compared with the measured results under the same operating conditions of experiments, that is, the minimum spark advance for best torque (MBT), volumetric efficiency of 80±2 %, air-fuel ratio of 15 and engine speed of 1000 rpm, with various torch nozzle areas and an open chamber. Consequently, the flow and combustion characteristics calculated for the S.I. engine with and without prechamber are discussed to examine the effect of torch jet on the velocity vectors, contour maps of turbulence and gas temperature.

To obtain a better understanding of the effect of torch nozzle area on the turbulent flame propagation in a spark ignition engine with an unscavenged prechamber, the combustion characteristics are analyzed from ensemble-averaged pressure diagrams, and the turbulent flame propagation in both the pre- and main chambers are observed using a high-speed camera with image-processing. Also, a numerical simulation is attempted by applying a k-ε model of turbulence to the two-dimensional unsteady flow field and an one-step irreversible reaction model to the combustion process. These engine experiments and numerical calculations are performed under the same operating conditions, that is, optimum spark advance for best torque (MBT), volumetric efficiency of ηv=80±2%, air-fuel ratio of A/F≃15 and engine speed of N ≃1000 rpm, with various torch nozzle areas (An). Consequently, the effect of torch nozzle on the flame propagation pattern become more clear.

To make clear the influence of a torch jet flow on the combustion process, a laser Doppler anemometer (LDA) is used to measure the mean velocity and turbulence intensity in a spark ignition engine with an unscavenged prechamber connected to a main chamber by a torch nozzle of different area sizes. The test engine is operated at a constant speed of 16.7 rps (1000 rpm), a constant volumetric efficiency of 80±2% and MBT for each torch nozzle area under firing as well as motored conditions. The LDA system is a dual beam forward scatter type, and its signals are acquired quickly and stored in a memory through a frequency tracking system. The LDA measurements are made at several locations in the main chamber. In the present paper, the turbulence is defined as the high frequency component of velocity above a cut-off frequency (0.75 kHz), and a cycle resolved analysis is performed to obtain the mean velocity and turbulence from individual cycle.

To examine the effect of torch jet direction on the combustion characteristics and engine performances, a spark-ignition engine with each divided chamber having a torch nozzle of different flow direction is used by changing the torch nozzle area, prechamber volume and air-fuel ratio, while keeping the engine speed of 1000 rpm and the volumetric efficiency of ην ≃ (80 ± 2) % constant. Typical pressure diagrams for different torch jet directions are analyzed to obtain such combustion characteristics as the crank angles of combustion start and finish, heat release rate and mass burned fraction. The engine performances, e.g. mean effective pressure and specific fuel consumption, are also measured. As a result, it can be made clear not only the effect of torch jet direction on the combustion characteristics, but also the relationship between the combustion characteristics and the engine performances for different torch jet directions.

To obtain a more reasonable model of torch combustion in a spark ignition engine with a vertical or horizontal prechamber, the instantaneous temperatures of combustion gas are measured by an infrared absorption-emission pyrometer with a narrow band pass filter for CO2 gas, while changing the torch nozzle area and air-fuel ratio. The gas temperature diagrams indicate that the ignition timing, flame propagation and combustion duration in the main chamber with vertical prechamber differ entirely from those with horizontal one. The fact is verified by comparing them with the heat release rates obtained from the pressure diagrams and with the flame propagation taken by means of high-speed photography. The measured gas temperature diagrams are, therefore, found to provide a lot of useful and local information concerning the combustion process and the engine performance in the prechamber engines.