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This paper is based upon the premise that the best way to deal with current constraints imposed upon car engines is by technological advances designed to (1) minimize pollutant emissions, (2) maximize engine efficiency, and (3) optimize tolerance to a wider variety of fuels. A sense of direction for such advances is derived from a critical assessment of the fundamental advantages of reciprocating I.C. engines as prime movers for automobiles, and the review of their recent developments. On this basis it is shown that major impact in this respect could be made by control1ed combustion. Intrinsically, this should involve proper handling of active radicals, the essential elements of the combustion reaction. Practically, this can be achieved by a variety of means, such as charge stratification, exhaust gas recirculation, homogeneous lean burn, combined with enhanced ignition and enhanced auto-catalysis.

THE WORK REPORTED in this paper is part of an on-going study of cyclic variability in spark-ignition engines. In order to analyze knock and its variability from cycle to cycle in a meaningful way, an algorithm has been developed to characterize the severity of the bulk pressure change associated with knocking combustion. This algorithm depends on the third differential of pressure over the period when autoignition might occur. A large negative value of third differential indicates the abrupt pressure rise and narrow pressure peak commonly associated with end gas autoignition. This knock diagnostic has the advantage of working on a low frequency data acquisition rate (1 point/CA° or less) and of producing consistent results in spite of high frequency noise on the pressure signal such as might be caused by resonance of a spark plug-mounted pressure transducer.

In a previous paper, a knock indicator based on the third derivative of the cylinder pressure trace has been developed. This knock indicator measures the rate at which pressure trace curvature changes from positive to negative during the knock peak. Since it is dealing only with the general shape of the pressure trace, it gives a measurement of combustion severity based on low frequency data such as is commonly used for engine cycle analysis. This low frequency sampling makes it useful for adding knock analysis to existing engine analysis programs without changes of equipment or significant increases in computational effort. It may also make it useful for future on-board engine controls using limited frequency response or heavily filtered pressure transducers. Results of using this knock indicator as a diagnostic tool on a multi-cylinder engine with a spark plug-mounted transducer are presented.