A numerical and experimental study of dual fuel diesel engine for different injection timings

The dual-fuel (diesel/natural gas, NG) concept represents a viable solution to reduce emissions from diesel engines by using natural gas as an alternative fuel. Dual fuel operation is characterized by a diesel pilot injection to start combustion in an intake port premixed NG/air mixture. Dual-fuel technology has the potential to offer significant improvements in the emissions of carbon dioxide from light-duty compression ignition engines. In these high-speed engines, where the combustion event can be temporally shorter, the injection timing can have an important effect on the performance and emissions of the engine [1]. This article summarizes the results of a combined numerical and experimental study on the effect of injection timing on performance and pollutant fractions of a common rail diesel engine supplied with natural gas and diesel oil. The study of dual-fuel engines that is carried out in this paper aims at the evaluation of the CFD potential to predict the main features of this particular technology. The experimental investigations represent a tool for validating such a potential and for highlighting, at the same time, the major aspects that arise from the actual engine operation with different diesel injection advance. In order to put into evidence the key phenomena that take place during the dual-fuel operation, say the typical flame propagation throughout the premixed methane-air medium that is activated by the early self-ignition of the diesel fuel, the fluid-dynamic calculations are extremely useful. The different conditions have been induced by different sets of the operating parameters and fuel; in particular, the tests have been performed by varying the injection timing at a fixed torque and diesel amount. Actually, the start of injection timing can considerably influence the combustion development and therefore THC and NOx fractions production. Preliminary calculations by using the Fluent code have been compared with the experimental data and a comparison between diesel and dual fuel diesel/CNG operation has been made, in terms of performance and pollutant levels.