Kazuhisa Mogi

Octane Appetite Studies in Direct Injection Spark Ignition (DISI) Engines

The anti-knock or octane quality of a fuel depends on the fuel composition as well as on the engine design and operating conditions. The true octane quality of practical fuels is defined by the Octane Index, Ol = (1-K)RON + KMON where K is a constant for a given operating condition and depends only on the pressure and temperature variation in the engine (it is not a property of the fuel). RON and MON are the Research and Motor Octane numbers respectively, of the fuel. Ol is the octane number of the primary reference fuel (PRF) with the same knocking behaviour at the given condition. In this work a wide range of fuels of different RON and MON were tested in prototype direct injection spark ignition (DISI) engines with compression ratios of 11 and 12.5 at different speeds up to 6000 RPM. Knock Limited Spark Advance (KLSA) was used to characterize the anti-knock quality of the fuel. Experiments were also done using two cars with DISI engines equipped with knock sensor systems. The anti-knock quality of a fuel in the car is inferred from the power/acceleration performance, which changes in response to knock. RON is dominant for fuel anti-knock quality at all engine speeds. Moreover, for low and moderate engine speeds, frequently used on the road, for a given RON, lower MON results in better fuel anti-knock quality.

Analysis and avoidance of pre-ignition in S.I. gasoline engines

Abstract In spark ignition gasoline engines, efforts to improve performance and exhaust emissions have resulted in increased compression ratios and methods of maintaining stoichiometric air-fuel ratio even at high engine load. This paper analyzes the pre-ignition phenomena under such tight conditions, and proposes a new method for avoiding pre-ignition. As a result of the analysis, it was shown that knocking occurred very frequently in the early stage of pre-ignition, which was caused by overheated spark plug or extremely hot combustion chamber deposits. It was also verified that the pre-ignition could be avoided by adding logic to the KCS (knocking control system) for screening high-frequency knocking to detect pre-ignition, and by quickly enriching the charged air fuel mixture after the detection.

Study on ion current and pressure behavior with knocking in engine cylinder

Abstract Knocking in a single-cylinder engine was analyzed by using the ion current and the pressure in several positions and the results of the combustion observation. The region where the ion probe catches the ions changes with the polarity and the power spectrum of the ion current did not always agree with that of the pressure. When the shock wave arrived at the ion probe, the ion current rapidly increased the same as the pressure. It was understood that the ion current vibrates because the ion density changes with coarseness and minuteness of the pressure wave.