Experimental investigation on a diesel engine operated in RCCI combustion mode

Low Temperature Combustion (LTC) concepts have been investigated in many recent studies, aiming to improve engine efficiency and minimize pollutant emissions. One of the most promising techniques is represented by the Reactivity Controlled Compression Ignition (RCCI), that can be obtained combining a low reactivity fuel (such as gasoline, natural gas, ethanol, etc) and a high reactivity fuel (such as Diesel oil). The former is injected in the intake manifold, and it generates a homogeneous mixture before the start of combustion; the latter is injected directly into the combustion chamber. This technology can be easily applied to existent Diesel engines, implementing a low pressure injection system for the low-reactivity fuel. This work presents the most important results of a preliminary experimental study, conducted on a light duty Diesel engine, modified in order to operate in RCCI combustion mode. In particular, four gasoline injectors have been installed between the intercooler and the intake plenum, while the injection strategy of both fuels has been optimized, along with boost pressure. Experiments show that at low loads it is possible to substitute most of Diesel fuel with gasoline, maintaining or even improving brake thermal efficiency. This result was obtained by optimizing the Diesel fuel injection strategy, without the support of EGR. However, at medium loads, it was not possible to achieve relevant reductions of Diesel fuel, due to the high risk of knocking.