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In-cylinder pressure of an IC engine is considered to be a major source of information about combustion process. It is a generally accepted method to obtain an in-cylinder pressure signal using a pressure sensor (transducer). In this paper, a different approach is presented. Information about the in-cylinder pressure can be obtained by measuring breakdown voltage across the spark-plug gap. A simple means for measurement of such voltage is developed. The breakdown voltage threshold depends on the density of the gas in the combustion chamber. A strong correlation between the measured breakdown voltages and in-cylinder pressure has been established.

A robust sliding mode control method is proposed for the design of a fuel injection control system, which can maxmize the conversion efficiency of 3-way conversion catalysts. For the purpose of developing and evaluating a fuel-injection controller, the mass of air in the intake manifold and actual fuel flow rate entering the combustion chamber are chosen as state variables of a 4-cycle MPI (Multi-Point Injection) gasoline engines. On the basis of the simulation results, we have manufactured the ECU (Electronic Control Unit) to operate the MPI gasoline engines and have experimented with 16-bit microprocessor computer. The experimental results show that the sliding mode fuel-injection controller can make the engine operate in the neighborhood of stoichiometric air/fuel ratio (14.7 ± 0.3) and can improve the conversion efficiency of 3-way catalyst more than 90%. Thus, it can satisfy current strict regulations about the automotive exhaust emissions.