THE COMMON-RAIL FUEL INJECTION TECHNIQUE IN TURBOCHARGED DI-DIESEL-ENGINES FOR AIRCRAFT APPLICTIONS

In the activity of injection mapping optimization, a good degree of knowledge on how a common rail injection works is strictly necessary. This paper is aimed to summarize the basic knowledge about turbocharged Common Rail Direct-injection Diesel engines (CRDID). It is possible to use automotive CRDIDs on aircrafts and helicopter; however their use is very different for the original car installation. For this reason a complete rethinking of the engine and the way the engine control is performed is strictly necessary. For this reason the engine should be reprogrammed for the new application. To perform this activity it is strictly necessary to know how the original automotive application works. This paper is aimed to this objective, in order to point out the differences with the automotive installation and the new optimization functions. The combustion process of turbocharged CRDID, equipped with high pressure common-rail fuel injection systems, with different boost pressures, injection pressures, and fuel quantities are introduced. The influence of the injection and the swirl mode on the ignition delay and the flame propagation is analyzed. The sac hole nozzles with a variable number of holes and different injector types (electromagnetic/piezoelectric) are also briefly described. An experimental analysis of the combustion process is briefly discussed along with spray penetration, dispersing angle, velocity, the distribution/evaporation of the fuel droplets, ignition delay, ignition location, combustion progression. The applied swirl has not an influence on the spray penetration, but it is extremely important for the ignition and the combustion process. On the contrary the swirl itself is reduced by the injected amount of high pressured fuel. The droplet turbulence increases from the center of the combustion chamber of the spray radial rapidly decreases. The difference in the combustion of CRDIDs, traditional diesel engines and spark ignition engine is also briefly discussed. Finally the difference from automotive and aircraft and helicopter CRDIDs, from the combustion tuning point of view is discussed. Optimum combustion (and mapping) is also introduced as basic concepts.