Influence of Early and Late Fuel Injection on Air Flow Structure and Kinetic Energy in an Optical SIDI Engine

Abstract

he turbulent in-cylinder air flow and the unsteady high-pressure fuel injection lead to a highly transient air fuel mixing process in spark-ignition directinjection (SIDI) engines, which is the leading cause for combustion cycle-to-cycle variation (CCV) and requires further investigation. In this study, crank-angle resolution particle image velocimetry (PIV) was employed to simultaneously measure the air flow and fuel spray structure at 1300 rpm in an optically accessible single-cylinder SIDI engine. The measurement was conducted at the center tumble plane of the four-valve pent-roof engine, bisecting the spark plug and fuel injector. 84 consecutive cycles were recorded for three engine conditions, i.e. (1) none-fueled motored condition, (2) homogeneous-charge mode with start of injection (SOI) during intake (50 crank-angle degree (CAD) after top dead center exhaust, aTDCexh), and (3) stratified-charge mode with SOI during mid compression (270 aTDCexh). The air flow structure (quantified by the objective metric-relevance index) and kinetic energy were examined to study the effect of the fuel spray on the air flow. The air flow was nearly identical for three conditions before the fuel injection. During fuel injection, the entrainment of air into the spray was observed near the spray but the flow structure further away from the spray was not significantly affected for both homogeneous and stratified charge modes. Right after the fuel was atomized, the spray increased the kinetic energy of air f low by 48 ± 25% and 45 ± 40% (average ± standard variation, with CCV included in standard deviation) for spray at intake and compression stroke, respectively. Spray changed the flow structure and kinetic energy immediately after injection for both conditions. The changes caused by injection during intake did not affect the flow and CCV at spark timing. For injection during mid compression, both the flow-structure and kinetic-energy CCV were apparently affected at spark timing. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE International.

Large Eddy Simulations with Conjugate Heat Transfer (CHT) modeling of Internal Combustion Engines (ICEs)

“…RI only compares the angle between two velocity vectors, while the kinetic energy is disregarded. To compare the kinetic energy between two velocity vectors, the local KEI can be used [49], and is calculated using…”

Manifold reduction techniques for the comparison of crank angle-resolved particle image velocimetry (PIV) data and Reynolds-averaged Navier-Stokes (RANS) simulations in a spark ignition direct injection (SIDI) engine

“…It would be useful, on the other hand, to have spatial information about how well the two flow fields are aligned and where the major differences occur. To achieve this, Chen et al 41 and Zhao et al 42 extended the idea of RI to point-to-point comparisons, and Zhao et al termed it as the Local Structure Index (LSI):…”

Quantitative metrics for comparison of in-cylinder velocity fields using particle image velocimetry

“…This metric can trivially be applied to each location within a pair of vector fields and subsequently spatially averaged to produce a single value that quantifies the match in alignment between two fields. The RI has been used to investigate the convergence of LES simulations of a GDI engine (Kuo et al 2014), to directly compare LES simulations to experimental results for model validation (Wang et al 2015) and to investigate the cyclic variability of PIV in-cylinder flow fields (Wang et al 2016) including the influence of fuel injection (Chen et al 2018). The RI has also been applied to quantify the differences in spray characteristics (Chen et al 2013a(Chen et al , 2014 and Proper Orthogonal Decomposition modes derived from PIV measurements (Chen et al 2012(Chen et al , 2013b.…”