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A single-cylinder, 500cc research engine was tested under Spark-Ignition (SI) and Controlled Auto-Ignition (CAI) operation with similar load and speed conditions. Camshafts with low-lift and short duration, run with a negative valve overlap, were used to obtain CAI at wide open throttle. Two different camshaft profiles were tested in order to get a wide span of loads at 1200 and 2000rpm. The SI engine was Port Fuel-Injected (PFI) while the CAI engine was tested with both PFI and an Orbital Air-Assist Direct-Injection (DI) system. To reduce the high Indicated Specific Nitrogen Oxide (ISNOx) emissions at λ=1, 10% External Exhaust Gas Residuals (EEGR) was applied to the SI engine. EEGR reduced ISNOx emissions and there was slight reduction in ISFC. However, when the engine was tested in CAI mode, both ISNOx and ISFC were lower than the SI engine.

The unsteady gas dynamic phenomena in engine intake systems of the type found in racecars have been examined. In particular, the resonant tuning effects, including cylinder-to-cylinder power variations, which can occur as a result of the interaction between an engine and its airbox have been considered. Frequency analysis of the output from a Virtual 4-Stroke 1D engine simulation was used to characterise the forcing function applied by an engine to an airbox. A separate computational frequency sweeping technique, which employed the CFD package FLUENT, was used to determine the natural frequencies of virtual airboxes in isolation from an engine. Using this technique, an airbox with a natural frequency at 75 Hz was designed for a Yamaha R6 4-cylinder motorcycle engine. The existence of an airbox natural frequency at 75 Hz was subsequently confirmed by an experimental frequency sweeping technique carried out on the engine test bed.

The unsteady gas dynamic phenomena in a racecar airbox have been examined, and resonant tuning effects have been considered. A coupled 1D/3D analysis, using the engine simulation package Virtual 4-Stroke and the CFD package FLUENT, was used to model the engine and airbox. The models were experimentally validated. An airbox was designed with a natural frequency in the region of 75 Hz. A coupled 1D/3D analysis of the airbox and a Yamaha R6 4-cylinder engine predicted resonance at the single-cylinder induction frequency; 75 Hz at an engine speed of 9000 rpm. The amplitude of the pressure fluctuation was found to be influenced by the separation between the intake pipes in the airbox. For an n-cylinder even-firing engine, if the intakes are coincident in the airbox, then the fundamental and all harmonics of the forcing function, apart from the (n-1)th, (2n-1)th, etc. will cancel. That is, only the multi-cylinder induction frequency and its multiples will not cancel.

This paper presents a discussion of the difficulties in evaluating the discharge coefficients of ports in the cylinder wall of high performance two-stroke engines. Traditionally such evaluation requires the knowledge of the area of the port on a chord normal to the direction of flow through the port. However, due to the complex shape of ports in these engines, it is difficult to know the exact flow direction without some kind of flow analysis. Results of a study conducted on various methods of obtaining the port area either by assuming a flow direction or using geometrical information are presented. From the information presented it can be seen that the use of wall area is quite acceptable to determine discharge coefficients. This wall area requires no interpretation by the experimenter and therefore also permits a direct comparison with other ports.