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The cycle-by-cycle variation of heat transferred per cycle (q) to the combustion chamber surfaces of spark ignition engines has been investigated for quasi-steady and transient conditions produced by throttle movements. The heat transfer calculation is by integration of the instantaneous value over the cycle, using the Woschni correlation for the heat transfer coefficient. By examination of the results obtained, a relatively simple correlation has been identified: This holds both for quasi-steady and transient conditions and is on a per cylinder basis. The analysis has been extended to define a heat flux distribution over the surface of the chamber. This is given by: where F(x/L) is a polynomial function, q″ is the heat transfer per cycle per unit area to head and piston crown surfaces and gives the distribution along the liner

Cycle-by-cycle pressure data have been recorded for a spark ignition engine operating over a wide range of steady state and perturbed running condition. The data base has been analysed to derive mass fraction burnt, pressure development and work mean effective pressure characteristics for individual cycles. Cross-correlation coefficients have been calculated to identify predominant relationships. The effect of combustion phasing on cross-correlation coefficients is particularly significant and three regimes of behaviour have been identified. These are associated with early, optimal and late cases. The cross-correlations between parameters derived from cycle-by-cycle data do not uniformly reflect trends seen between cycle-averaged values of these. Auto-correlation results have been examined for interactions between successive cycles with less success, although, again combustion phasing can have a significant influence on the strength of auto-correlation coefficients.

Experimental studies have been carried out on a spark ignition engine with port fuel injection to examine the influence of injector type and to contrast this with the effects of fuel composition. Intake port fuel transport characteristics and engine-out emissions for fully-warm and warm-up engine operating conditions have been examined as indicators of performance. The investigation has encompassed four types of injector and five gasoline blends. Fuel transport has been characterised using the τ and X parameters. The influence of injector type on these is of similar significance as that of changes in gasoline composition between summer and winter grades. The latter will limit the in-service accuracy of open-loop mixture control during transients. Injector type has a small effect on engine-out emissions under fully-warm operating conditions but has a significant influence on emissions during the early stages of warm-up.