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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.

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.

This paper describes a technique whereby race car airbox performance can be assessed directly in terms of predicted engine performance by coupling a one-dimensional engine model on a timestep-by-timestep basis to a three-dimensional computational fluid dynamics (CFD) model of an airbox. A high-performance three-litre V10 engine was modelled using Virtual 4-Stroke unsteady gas dynamics engine simulation software, while two airbox configurations, representative of those used in FIA Formula 1 (F1), were modelled using general purpose CFD software. Results are presented that compare predicted engine performance for the two airbox geometries considered in the coupled simulations. Individual cylinder performance values are also presented and these show significant variations across the ten cylinders for each airbox simulated.

The advantages of high power to density ratio and low manufacturing costs of a two-stroke engine compared to a four-stroke unit make it currently the most widely used engine type for 50cc displacement 2-wheelers. This dominance is threatened by increasingly severe exhaust emissions legislation, forcing manufactures to develop their two-stroke engines to comply with the legislation. This paper describes a simple solution to reduce these harmful emissions in a cost effective manner, for a scooter application. The method of stratified scavenging is achieved by delivering the fuel into the rear transfer passage from a remote mechanical fuel metering device, operated by intake manifold pressure. Air only is delivered into the cylinder from the remaining transfer passages which are directed towards the rear transfer port, thus impeding the fuel from reaching the exhaust during the scavenging process.

Analysis of pressure traces from within the cylinder of IC engines is a long established technique, particularly in automotive applications. This approach allows burn rate data to be calculated from the shape of the pressure traces, providing direct combustion information to development engineers. With the proliferation of high-powered and low-cost computers, recording of pressure traces and analysis to give burn rates are now becoming standard measurements. However, this is still a complex technique, which is very open to error and prone to misinterpretation of results. This is particularly relevant for two-stroke engines where cyclic variations can be high and traces can be difficult to analyze. This paper considers the standard techniques available for pressure trace analysis, highlighting the areas for problems and outlining good practice for reliable and accurate measurement.

The application of current CFD techniques to the crankcase of a conventional two-stroke engine is described. The model was based on a single-cylinder research engine and included features to simulate the motion of the reciprocating piston, the rotating flywheel, the reed valve and the opening and closing of the transfer ports. The model did not take account of the piston geometry and connecting rod, as their inclusion would have added undue complexity to this initial treatment of the problem. The resultant flow predictions were largely dominated by the flywheel induced recirculation. However, during the induction phase a strong ‘s’ shaped flow developed to carry the inlet charge directly through the crankcase and into the under-piston area.

This paper describes the operation and performance of two direct fuel injection strategies, namely a ram-tuned injection system (single fluid) and an air-assisted injection system (twin fluid). The injection systems are tested on a 500 cm3 single-cylinder cross scavenged two-stroke cycle engine during part load operation at 1600 rev/min. Particle sizing tests are presented for each injection system, in conjunction with specific emissions and performance results for firing engine tests.

A 500 cc single cylinder two-stroke engine employing cross scavenging and direct air-assisted gasoline injection is described. Preliminary engine test results are presented for 3000 rpm full load and 1600 rpm part load operating conditions. The effects of fuel injection timing on full and part load brake specific fuel consumption and exhaust emissions are examined.