Book Description

The main driving force behind this research was the need for cleaner and more efficient engines to meet the ever-increasing demands on the modern automobile's emissions. In recent years different studies have been carried out to analyze the combined effects of high-pressure injection, boost pressure, multiple injections, included spray angle and combustion chamber geometry. Though considerable research has shown these technologies can meet the low emission regulations, the careful optimization of the engine operating conditions is still required in order to get the full benefit of the different strategies. With these issues as motivation, the first important objective of this study was to gain a detailed understanding of the mechanisms through which fuel injection interacts with other engine parameters and influences diesel combustion and emissions, and hence to attempt to generalize the adoption of multiple injection strategies with regards to improving diesel engine performance. For this purpose, a modified parameter called "Homogeneity Factor of in-cylinder charge" (HF) was introduced and proposed as a new measure in combustion theory to analyze the combustion characteristics and air-fuel mixing process of diesel engines in more detail. The second part of this research builds upon a detail investigation on the included spray cone angle concept and explores further their use in conjunction with multiple-injection strategies in diesel engines. In addition, an investigation was performed in third phase of this research to analyze the effects of piston geometry on combustion, performance and exhaust emission characteristics. The results showed that employing a post-injection combined with a pilot injection results in reduced soot formation from diffusion combustion and enhances the soot oxidation process during the expansion stroke, resulting in decreased soot emissions, while the NOx concentration is maintained in low levels. It was also found that spray targeting is very effective for controlling the in-cylinder mixture distributions especially when it accompanied with advanced injection strategies. Moreover, the results confirmed that a narrower width of piston bowl has a higher unburned fuel air mixture region and hence results in higher soot emissions but with slightly larger piston surface area the optimum operating point could be obtained.