Evaluation of a PCCI combustion in euro VI diesel engines

Abstract

Currently, the world is facing two crises from the point of view environmental: the scarcity of fossil fuels and environmental degradation. According to projections by 2020 the use of vehicles would triple and also increase demand for fossil fuel and therefore emissions contaminants. Compared with the gasoline engine, diesel engine has the advantage of being a more efficient engine and therefore emits less CO2. However, produce high levels of NOx and particulates. To address these difficulties, we have proposed different actions. One solution, constitute the advanced concepts of combustion Diesel. These concepts allow to reduce levels of NOx and particulates. However, have the disadvantage of producing high levels of noise combustion, the early use of injections, which cause a more fuel is burned in premixed conditions. However, NOx emissions increased in most operating conditions. On that way, various technologies have been introduced to reduce emissions from diesel engines, the in-cylinder reduction techniques of PM and NOx like low temperature combustion (LTC which is an important field of research and development of modern diesel engines. Furthermore, increasing prices and question over the availability of diesel fuel derived from crude oil have introduced a growing interest. Hence it is most likely that future diesel engines will be operated on pure biodiesel and/or blends of biodiesel and crude oil-based diesel. Being a significant technology to reduce emissions, LTC deserves a critical analysis of emission characteristics for both diesel and biodiesel. We can divide LTC in two categories, field of our study. Those in which the combustion phasing is decoupled from the injection timing and the kinetics of the chemical reactions dominate the combustion, are in the first category which is known as HCCI mode. In the second category, combustion phasing is closely coupled to the fuel injection event which is termed as PCCI mode. PCCI combustion seeks to obtain a fully premixed charge before the start-of-combustion, which will result in fully premixed combustion. By injecting very early in the cycle, the air and fuel mix thoroughly such that, upon combustion of the mixture, there are no locally rich regions and little PM is formed. PCCI combustion differs slightly from pure HCCI combustion in that the direct fuel injection results in minor air-fuel mixture gradients, and thus the mixture is not truly homogeneous. Start of combustion is initiated by auto-ignition of the mixture when a sufficiently high cylinder temperature is attained during the compression stroke. When the auto-ignition occurs, the combustion takes place nearly instantaneously throughout the cylinder. The application of PCCI combustion suffers from several practical problems. First, because the mixture combusts almost instantaneously, the heat release is very rapid. If the auto-ignition occurs too far Before Top Dead Center (BTDC), this rapid heat release results in very high cylinder pressure rise rates, and high peak cylinder pressures. In addition, this rapid heat release tends to expose the in-cylinder nitrogen and oxygen to prolonged high temperatures, which can lead to high NOx formation rates. Second, early injection can result in spray impingement on combustion chamber wall surfaces, since the spray penetration is increased at the low gas densities in the chamber early in the compression stroke. However, perhaps the biggest challenge with PCCI combustion is control. This makes emissions control, and overall engine control, very difficult. In conclusion, the aim of this project is to open a field of knowledge of one of the most advanced new combustion concepts in low-temperature combustion, the PCCI combustion technology, which is already an important implantation via research and development in the field of the automotive industry