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The location of the peak pressure can serve as a control parameter to adjust ignition timing and optimize engine performance. The ionization sensor, an electrical probe for combustion diagnostics, can provide information about the peak pressure location. However, the reliability of such information is rather poor. In-cylinder gas flow at the electrodes may be one reason for this. We present results from an investigation of the relationship between ionization sensor current and pressure under various gas flow conditions. The gas flow velocity in the vicinity of the electrode gap was measured by LDA. From the results one may infer how the in-cylinder gas flow affects the reliability of the prediction of pressure peak location from the ionization sensor signal. One finding is that high bulk gas flow impairs the precision of the prediction in certain configurations.

Laser sheet droplet illumination was used to visualize the concentration of fuel droplets over the piston top area. Four different cylinder designs were examined: Open transfer channels and three types of cup handle transfer channels. Optical access to the scavenging area of the engine was achieved by removing the silencer and use a window in the top of the engine. The engines were run at their rated speeds: 9000 rpm for three of the engines and 5800 rpm for one of them. Images of the concentration patterns were captured at various crank positions, −20, −10, 0, 10, 20, 30 Crank Angle Degrees (CAD) from Bottom Dead Center (BDC). Results show that the concentration of fuel droplets is higher close to the back wall of the cylinder with cup handle transfer channels. Late in the scavenging phase, the concentration pattern is more spread over the entire cylinder area, for all types of transfer channels.

This paper is a direct continuation of a previous study that addressed the performance and design of a variable compression engine, the Alvar-Cycle Engine [1]. The earlier study was presented at the SAE International Conference and Exposition in Detroit during February 23-26, 1998 as SAE paper 981027. In the present paper test results from a single cylinder prototype are reviewed and compared with a similar conventional engine. Efficiency and emissions are shown as function of speed, load, and compression ratio. The influence of residual gas on knock characteristics is shown. The potential for high power density through heavy supercharging is analyzed.