An increasing interest in the use of natural gas in CI engines is currently taking place, due to several reasons: it is cheaper than conventional Diesel fuel, permits a significant reduction of carbon dioxide and is intrinsically clean, being much less prone to soot formation. In this respect, the Dual Fuel concept has already proven to be a viable solution, industrially implemented for several applications in the heavy duty engines category.
An experimental research activity was devoted to the analysis of the potentiality offered by the application of a Dual Fuel Diesel-CNG configuration on a light duty 2L Euro 5 automotive diesel engine, equipped with an advanced control system of the combustion. The experimental campaign foresaw to test the engine in dynamic and steady state conditions, comparing engine performance and emissions in conventional Diesel and Dual Fuel combustion modes. To this aim, dynamic engine tests were performed adopting the New European Driving Cycle (NEDC) while eight steady-state operative test points, representative of the engine working during the homologation cycle, were chosen to analyze specific aspects of the Dual Fuel combustion process. The engine was fully instrumented for indicating signal analysis and pollutant emission measurements.
The study confirmed the generally assessed results in terms of strong smoke and CO2 reduction and significant total hydrocarbon emissions (mainly methane) increment when a gaseous fuel is burned in Dual Fuel mode. Due to the high methane emissions at low loads that limits the CNG substitution ratio with diesel, the application of the DF concept is still critical for automotive engines. Moreover, the combustion analysis gave important information on the critical and beneficial aspects of the management engine control technology when this innovative combustion concept is adopted.