Experimental investigation and combustion analysis of a direct injection dual-fuel diesel-natural gas engine

A single cylinder diesel engine has been converted into a dual fuel engine to operate with natural gas together with a pilot injection of diesel fuel used to ignite the CNG-air charge. The CNG was injected into the intake manifolds via a gas injector on purpose designed for this application. The main performance of the injector such as flow coefficient, instantaneous mass flow rate, delay time between electrical signal and opening of the injector, have been characterized by testing the injector in a constant volume optical vessel. The CNG jet structure has also been characterized by means of shadowgraphy. The engine, operating in dual fuel mode, has been tested on a wide range of operating conditions spanning different values of engine load and speed. For all the tested operating conditions, the effects of CNG and diesel fuel injection pressure, together with the amount of fuel injected during the pilot injection, were analyzed on the combustion development and the consequences on the engine performance, in terms of specific emissions and fuel consumption