The interest in Natural Gas (NG) as alternative fuel for transportation is constantly growing, mostly due to its large availability and lower environmental impact with respect to gasoline or diesel fuel. In this scenario, the application of the Dual Fuel (DF) Diesel- Natural Gas (NG) combustion concept to light duty engines can represent an important route to increment the diffusion of natural gas use. Many studies have proven the benefits of DF with respect to conventional diesel combustion in terms of CO2, NOx, PM and PN emissions, with the main drawback of high unburned hydrocarbon, mainly at low/partial engine loads. This last aspect still prevents the application of DF mode to small displacement engines.
In the present work, a 2.0 L Euro 5 compliant diesel engine, equipped with an advanced electronic closed-loop combustion control (CLCC) system, has been set up to operate in DF mode and tested on a dyno test bench. The experimental campaign was performed in steady-state engine conditions and organized in two phases. Firstly, the aim was to identify optimal values of NG substitution ratios in several engine operating points. Secondly, a thorough analysis of the effects of many engine control parameters (e.g. NG substitution ratio, diesel pilot injection strategies, EGR) on DF combustion evolution was performed, at low and medium engine load.
A strong potential on THC emissions control was assessed for parameters like combustion phasing and EGR, giving rise to wider margins of engine recalibration, in comparison with the standard Diesel calibration. The research activity will permit to identify an optimized DF working map, tailored for an automotive multi-cylinder Diesel engine, and to evaluate the actual applicability of the DF configuration on the selected combustion system.