In-Cylinder Combustion Studies of Diesel-Compressed Natural Gas Dual Fuel with Increasing Energy Fraction and Its Effect on Emissions

Compressed natural gas (CNG) is a promising alternative fuel for compression ignition (CI) engines under dual-fuel (DF) mode operation. Its application on commercial heavy-duty multicylinder diesel engines is scarcely reported, and its potential usage is investigated through a research study. The focus of this research was to study the in-cylinder combustion and its effect on emissions with an increasing energy fraction of CNG at different speeds (1000 rpm-2500 rpm) and load conditions (Speed-Torque mode), inducted through the intake manifold at different mass flow rates ranging from 0.67 kg/h to 4.0 kg/h corresponding to an energy substitution rate (ESR) of 1.9%-60.2% while using diesel as pilot fuel. In-cylinder pressure, heat release rate (HRR), and pressure rise rate (PRR) increased with the increase in CNG mass flow rate (CMFR). Combustion duration is prolonged under diesel-CNG DF (DDF) mode while ignition delay (ID) is reduced with an increase in CNG flow rate. Carbon monoxide (CO) and total hydrocarbon (THC) emissions reduced with a longer fuel burn rate (FBR), combustion duration, and diesel injection duration (DID), and was lower at higher indicated mean effective pressure (IMEP) alternately; nitric oxides (NOx) and carbon dioxide (CO₂) emission were lower at shorter above combustion parameters. The combustion characteristics of DDF engines and their effect on emission performance have been studied and used for the optimization of the heavy-duty diesel engine.