Influence of tumble and TKE on combustion, fuel economy, and emissions of a single cylinder motorcycle engine

Abstract

The impact of gasoline engines on improving fuel consumption and reducing emissions has received increasing attention around the world, and emissions regulations have become stricter. However, complex techniques in engine improvement increase costs. The purpose of this study is to develop or improve the design of the intake geometry without additional cost to improve the engine thermal efficiency, thereby improving fuel economy and emissions. In this study, emissions and fuel consumption of a 125 c.c. commercially available motorcycle was investigated. In addition to modifying the intake and valve angles and maintaining the intake air volume, a software for computational fluid dynamics (CFD) was used for steady-state and transient analysis of the in-cylinder flow field, tumble ratio and turbulence kinetic energy (TKE), and the results were compared with the data of the experimental platform. The burn duration of the engine, indicated mean effective pressure (IMEP), indicated specific total hydrocarbons (ISHC), nitrogen oxide (ISNOx) and carbon monoxide (ISCO) were measured on the bench. The transient predicted results show that the tumble ratio is a maximum increase of 27.82% at 656 crank angle (CA) degrees near the top dead center (TDC) on the compression stroke. In the ignition area within 5°–20° before top dead center (BTDC), average of the turbulence kinetic energy (TKE) was 120.37 m2/s2, distributed hot area was wide and close to the ignition position. In the steady-state measurement, it was verified that the tumble ratio was significantly improved by modifying inlet, the same trend as the analysis result. In the bench test for full load measurement, the average of IMEP increased by 10.92%, indicated specific fuel consumption (ISFC) improved by 11.7%, burn duration increased by 25.27%, ISCO improved by 43.41%, and ISHC improved by 64.33%. For portion load measurement, the average of ISFC improved by 2.16%, burn duration increased by 24.84%, ISCO improved by 43.44%, ISHC improved by 17.7% and ISNO improved by 12.89%. Based on the results, the tumble and TKE were improved by optimizing the angle between the intake valve and the intake port. The ISFC of model B was significantly improved under the two states. The ignition delay time was longer, and the overall burn duration was much improved. When it came to emissions, the ISCO and ISHC were significantly improved, and the ISNO was much higher at full load but lower at partial load due to the engine temperature and engine loads. At partial loads, the high tumble did benefit the combustion, fuel economy and emissions of a single-cylinder motorcycle engine.