Abstract
Dimethyl ether (DME)/diesel blended fuels are used to improve the emissions caused by spray wall impingement during the early injection period. However, experimental results have showed that the spray wall impingement still cannot be avoided due to the engine structure and low density of the in-cylinder charge at the early injection timing. Furthermore, the wall film formed in the spray wall impingement process directly affects fuel/air mixture formation, combustion, exhaust emissions and oil quality subsequently. In this paper, the wall film distribution of DME/diesel blended fuels formed during the spray wall impingement process has been experimentally investigated. The variations of wall film distribution, wall film area and average thickness with different injection pressures, impingement distances, impingement angles and blending ratios have been discussed under both dry wall and wet wall conditions. Results showed that the wall film distribution styles were mainly determined by the spray impingement momentum. The variation of the wall film area and average thickness were affected by three factors including the impingement momentum, wall film mass and fuel properties. Correlation analysis was introduced in order to evaluate the effect of each impact factor on the variation of wall film area and average thickness.
Highlights
Numbers of advanced combustion technologies have been studied in order to solve the NOx and soot trade-off problem of the conventional diesel engine, such as homogeneous charge compression ignition (HCCI) and premixed charge compression ignition (PCCI) combustion
Kolodziej et al [6] indicated that advancing the early injection timing increased the mass and number of particulate matter (PM) emission, which was attributed to the increasing amounts of fuel deposited on the piston head
This paper experimentally investigated the wall film characteristics of the Dimethyl ether (DME)/diesel blended fuels formed in the spray wall impingement duration
Summary
Numbers of advanced combustion technologies have been studied in order to solve the NOx (nitrogen oxide) and soot trade-off problem of the conventional diesel engine, such as homogeneous charge compression ignition (HCCI) and premixed charge compression ignition (PCCI) combustion. Early injection will cause some fuel spray unavoidably impinging on the cylinder wall or piston head resulting in the formation of wall film due to the low gas density at the early injection timing [4,5]. In order to improve the emission level of the diesel engine using early injection strategy and reduce the occurrence of spray wall impingement, alternative fuels have drawn considerable research attention recently. With the advanced injection timing strategy, the HC and CO emissions still increased which was mainly because of unavoidable spray-impingement on the cylinder walls. Because of the unavoidable spray wall impingement, considerable work has been published in recent years about the wall film characteristics These are mainly focused on the pure diesel or gasoline fuels.
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