Abstract
An investigation into in-cylinder swirl and tumble flow characteristics with reduced maximum valve lifts (MVL) is presented. The experimental work was conducted in the modified four-valve optical spark-ignition (SI) test engine with three different MVL. Particle image velocimetry (PIV) was employed for measuring in-cylinder air motion and measurement results were analyzed for examining flow field, swirl and tumble ratio variation and fluctuating kinetic energy distribution. Results of ensemble-averaged flow fields show that reduced MVL could produce strong swirl flow velocity, then resulted in very regular swirl motion in the late stage of the intake process. The strong swirl flow can maintain very well until the late compression stage. The reduction of MVL can also increase both high-frequency and low-frequency swirl flow fluctuating kinetic energy remarkably. Regarding tumble flow, results demonstrate that lower MVLs result in more horizontal intake flow velocity vectors which can be easily detected under the valve seat area. Although the result of lower MVLs show a higher tumble ratio when the piston is close to the bottom dead centre (BDC), higher MVLs substantially produce higher tumble ratios which can be confirmed when most cylinder area lies in the measuring range.
Highlights
In recent years, advanced combustion technologies like gasoline direct injection (GDI) [1], gasoline CAI [2], etc. have made significant contributions to improving the fuel economy of gasoline engines and for reducing CO2 emissions, in particular with support from variable valve actuation (VVA) [3,4] which has played a critical role in enhancing the combustion performance of gasoline engines
A particle image velocimetry (PIV) system including necessary data analysis has been applied for examining swirl and tumble flow field, swirl and tumble ratio variation and fluctuating kinetic energy distribution
‚ Under the present measurement conditions, PIV investigation results showed that reduced maximum valve lifts (MVL) could enhance swirl flow velocity, which resulted in a very regular swirl motion in the late stage of the intake process and the strong swirl flow can maintain very well until the late compression stage
Summary
In recent years, advanced combustion technologies like gasoline direct injection (GDI) [1], gasoline CAI (controlled auto-ignition) [2], etc. have made significant contributions to improving the fuel economy of gasoline engines and for reducing CO2 emissions, in particular with support from variable valve actuation (VVA) [3,4] which has played a critical role in enhancing the combustion performance of gasoline engines. In an initial measurement on a steady flow test rig with the same cylinder head as used in the following investigation, results (as shown in Figure 1) have demonstrated that reduced MVL could significantly enhance in-cylinder swirl motion, but simultaneously reduce tumble motion strength With those influences of VVL on in-cylinder flows, it will be necessary to investigate how air-fuel mixing and combustion would be affected under those conditions. It has been reported in some research on diesel engines that air-fuel significantly enhance in‐cylinder swirl motion, but simultaneously reduce tumble motion strength Figure 1F. iIgnufrleu1e.nIcnefluoefnrceedouf creedducmedaxmiamxiummumvavlavlveelliiffttss ((MMVVL)Lo)notnhethsweisrlwrairtiloraantdiotuamndbleturamtiobluendraertio under steady flsotewadmy fleaowsumreemasuenretm. ent
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