Search Results

The effect of the electrodes on the early signal of the ionization sensor has been studied experimentally and with a model for the sensor. Experiments in a constant-volume combustion chamber with a generic electrode configuration allowed to investigate the role of electrode contact and the main path of the current. A framework for a model allowing the inclusion of electrode processes is introduced, and a first implementation of this model is presented. The results from the simulations are in good qualitative agreement with the experimental observations. Our conclusion is that electrode processes can limit the current during early combustion, and that the geometry of the electrodes, and especially the cathode, govern the characteristic shape of the first current peak.

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.

A combined experimental and theoretical effort has been made to identify the most important contributors to equilibrium ionization in the post-flame gas. In the past, nitric oxide (NO) has always been assumed to be the main electron donor in the compressed hot post-flame gases. However, correlations observed between the amount of NO in the exhaust gases and the current amplitude may be deceiving due to the fact that both the formation of NO and the ionization process are strongly temperature dependend. The temperature-current relationship in data from various experiments in constant volume combustion chambers and engines was utilized to check the hypothesis that NO acts as the major contributor to ionization. Based on a well-motivated model for the current, the effect of temperature and electron donor concentration has been separated.