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We have developed a new engine roughness tester which is capable of monitoring the spark plug voltage and crankshaft speed fluctuation as well as detecting the misfire of the SI internal combustion engine. In order to detect misfire, the newly developed “spark plug voltage analysis method” is combined with the conventional “crankshaft speed fluctuation method”. It is capable of logging ordinary data, determining the waveform for a detection / misfire

The corelation between flame ion density and engine operating condition, such as air fuel ratio mixture and cylinder pressure peak value, etc., is commonly known. However, due to the difficulty of ion probe installation in the engine and the interruption of the high voltage ignition spark, the ionization current method is not optimally utilized. This paper presents the Spark Plug Voltage-ion method which requires a minor modification to the ignition system and will indirectly detect flame ion density. The voltage sensor is a voltage divider by capacitance which measures the spark plug voltage. The resulting behavior of the voltage wave form is noteworthy. After spark discharge, the stored residual charge of the spark plug starts to discharge by ion in a flame. Therefore, ion density in a flame is detected by the decay time of spark plug voltage.

The idea to monitor the combustion in an internal combustion engine and using the obtained data to control combustion in the engine has been around for some time now. There are two well-known methods, although in the capacity of lab experiments, which had been developed under this principle. One features the analysis of combustion pressure and the other features the analysis of ionic currents detected in the combustion gas. Although highly precise analysis can be achieved by the former, there are problems in the installation of sensors for detecting combustion pressure, also in the durability and cost of such sensors. As for the latter, there are also problems in installing sensors for detecting the ionic currents and the reliability of obtained data from such sensors is still questionable.

As technologies for simultaneously maintaining the current high thermal efficiency of diesel engines and reducing particulate matter (PM) and nitrogen oxide (NOX) emissions, many new combustion concepts have been proposed, including premixed charge compression ignition (PCCI) and low-temperature combustion[1]. However, it is well known that since such new combustion techniques precisely control combustion temperatures and local air-fuel ratios by varying the amount of air, the exhaust gas recirculation (EGR) ratio and the fuel injection timing, they have the issues of being less stable than conventional combustion techniques and of performance that is subject to variance in the fuel and driving conditions. This study concerns a system that addresses these issues by detecting the ignition timing with in-cylinder pressure sensors and by controlling the fuel injection timing and the amount of EGR for optimum combustion onboard.