Search Results

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.

Computational Fluid Dynamics (CFD) is frequently used to predict complex flow phenomena and assist in engine design and optimization. The scavenge process within a 2-stroke engine is key to engine performance especially in high performance racing applications. In this paper, FLUENT CFD code is used to simulate the scavenging process within a 125cc single cylinder racing engine. A variety of different port designs are simulated and scavenge characteristics compared and contrasted. The predicted CFD results are compared with measured scavenge data obtained from the QUB single-cycle scavenge rig. These results show good agreement and provide valuable insight into the effect of port design features on the scavenging process.

The harsh environment presented by engines, particularly in the exhaust systems, often necessitates the use of robust and therefore low bandwidth temperature sensors. Consequently, high frequencies are attenuated in the output. One technique for addressing this problem involves measuring the gas temperature using two sensors with different time-constants and mathematically reconstructing the true gas temperature from the resulting signals. Such a technique has been applied in gas turbine, rocket motor and combustion research. A new reconstruction technique based on difference equations has been developed and its effectiveness proven theoretically. The algorithms have been successfully tested and proven on experimental data from a rig that produces cyclic temperature variations. These tests highlighted that the separation of the thermocouple junctions must be very small to ensure that both sensors are subjected to the same gas temperatures.

The improvement of computer simulation packages with experimentally validated sub-models has benefited the engine designer in reducing development time and costs. Such packages offer invaluable information regarding the internal gas dynamics and gas exchange characteristics. Presented are measured dynamometer results of a RS Honda 125 cm3 two-stroke single-cylinder motorcycle grand prix road-racing engine operating at full throttle from 9000 rev/min to 13000 rev/min. The engine is instrumented to provide in-cylinder and exhaust pipe pressure crank-angle histories. All relevant engine geometry, discharge coefficients, scavenging characteristics and combustion data are used to simulate the engine using a one-dimensional (1-D) engine simulation package. In-cycle crankshaft angular velocity fluctuations are also considered. Performance parameters such as power, BMEP and delivery ratio, together with pressure diagrams are compared to the measured data.

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.