Abstract
The need to reduce CO2 emissions of modern diesel powertrains will be intensified in the near future, because of the current European legislation for CO2 emissions and the rising shortage of fossil energy sources. Using alternative fuels, extracted from biomass, has a high potential to reduce CO2 emissions from well to wheel.
A possibility to optimize the mixture formation is the increasing of the injection pressure. The produced spray leads to an optimized mixing of fuel and air and an improved combustion process involved which results in reduced specific fuel consumption and soot emissions. In combination with a rising exhaust gas recirculation, the increasing injection pressure leads to an additional reduction of the nitrogen oxides emissions.
The employment of alternative fuels with simultaneous optimizing the mixture formation presents an important mean to reduce the fuel consumption of modern diesel engines. A high pressure injection system”, which is able to inject with very high injection pressures, is developed in the project “Ultra High Pressure Injection of Alternative Diesel Fuels”. Simultaneously a pressure chamber has been refitted for diesel operation in which a chamber pressure and temperature level can be realized up to 60 bar respectively 500 °C. Ambient conditions like in the combustion chamber of a charged diesel engine during the injection time can be described.
The paper presents results of the spray behaviour, which were measured in a pressure chamber with optical measuring devices at conditions like in the engine. Using a high-speed camera, the macroscopic structure of the spray (spray angle, penetration) will be investigated at different injection pressures, chamber pressures and temperatures and for different alternative fuels. By variation of the fuel and the injection parameters tendencies about the behaviour of the mixture formation with alternative fuels under engine conditions can be derived. With the help of these results statements can be defined for constructive modifications of the nozzle parameters which are important for the mixture formation, like the diameter and the number of nozzle holes, conicity or the rate of rounding to optimize the spray characteristic. Furthermore the high-speed investigations are important for the definition of the geometric measuring locations in relation to the following measurement with particle dynamic analysis (PDA).
The paper presents the main results of the investigations and concludes with an outlook to ongoing research activities.
Keywords: Ultra high pressure injection, alternative diesel fuels, spray investigations, pressure chamber, laser optical measurement devices