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Spray development and fuel-air mixture formation are important process early in diesel combustion. Moreover, wall impingement of spray and spray interaction also affect combustion process greatly. The spray interaction happens in multi-hole injector. This study investigated influence of spray combustion accompanied with wall impingement and spray interaction on heat release history. The experiment observed initial spray development by shadowgraph technique using a constant volume spray chamber. The injectors were a single-hole injector and multi-hole injectors with the hole-number of 8, 6 and 4. The combustion experiment observed flame development. The spatial distribution of the flame temperature and the soot oxidation were analyzed by the flame images. Results of the unburned spray images revealed the difference of mixture formation and initial combustion between single-hole and multi-hole sprays.

The aim of this study is to clarify the mixture formation in the combustion chamber of our developed natural gas engine incorporating the sub-chamber injection system, in which natural gas is directly injected into a combustion sub-chamber in order to completely separate rich mixture in the sub-chamber, suitable for ignition, from ultra-lean mixture in the main chamber. Mixture distributions in chambers with and without sub-chamber were numerically simulated at a variety of operating conditions. The commercial software of Fluent 16.0 was used to conduct simulations based on Reynolds averaged Navier-Stokes equations in an axial 2 dimensional numerical domain considering movements of piston. Non-reactive flow in the combustion chamber was simulated before the ignition timing at an engine speed of 2000 rpm. The turbulence model employed here is standard k-ε model. Air-fuel ratio is set with a lean condition of 30.

It is well known that indirect injection (IDI) diesel engines have better exhaust performance but lower fuel economy than direct-injection (DI) diesel engines. In recent years, fuel efficiency has been strongly demanded to reduce global warming. Therefore, the IDI engine is required to reduce fuel consumption. According to past research, fuel injection control can be one of the means to improve fuel efficiency in the IDI system. This paper tried to apply two-stage fuel injection as one of the fuel injection control methods to improve fuel efficiency while suppressing exhaust emissions. Particularly, since it is considered necessary to reduce the amount of injection during the ignition delay period in the sub-chamber with the IDI type, two-stage injection with a small amount of pilot injection was applied.

This study tries to reduce SOF (Soluble Organic Fraction) emissions at low load by improving spray characteristics of rape-seed oil and avoiding wall-impingement of the spray to the piston wall in a real direct-injection diesel engine applying rape-seed oil directly. High swirling air motion and squish flow caused by the piston configurations are taken as measures. Further, flat bottom shape of the piston is applied. Results show that emissions can be improved by the support of air motions. High swirl with toroidal piston is effective to reduce SOF emissions. Re-entrant piston with flat bottom shape offers the best emission performance. Raising gas temperature is also effective to reduce SOF emissions at low load.

A fundamental study on spray behavior for small quantity injection under high boosting and high temperature conditions was carried out by applying dual nano-spark shadowgraph photography method to constant volume spray chamber filled with inert gas. The study showed macro-scale and micro-scale spray structures and dynamic changes of diesel spray affected by ambient density and temperature right after the pilot injection. Detailed observation and analysis of the images showed that high density surrounding gas decreases the mainstream velocity of the spray after injection, which restrains air entrainment into the spray. There is a change of flying direction of the droplets at spray boundary under high density condition. Many droplets move outward from the spray after the lapse of time. Spray evaporation is promoted by vaporization of droplets at spray boundary. High density condition greatly promotes droplets evaporation at spray boundary.