Investigation of Performance and Exhaust Emissions of Compressed Natural Gas-Diesel Dual-Fuel Engine under Different Engine Speed and Load Conditions

Compressed Natural Gas (CNG) is a promising alternative fuel for application in diesel engines operating on dual-fuel mode. However, its application for a commercial heavy-duty engine has been limited due to difficulty in modification and in altering the engine control unit (ECU) settings. In this investigation, an attempt has been made to optimize the CNG flow rate for different speed and load conditions for operating a commercial heavy-duty turbocharged intercooled engine under diesel-CNG dual fuel based on engine performance and emission parameters on an eddy current engine dynamometer. CNG was inducted through the intake manifold at varying mass flow rates of 0.65-4.0 kg/hr for different speed and load conditions while operating the engine at the Speed/ Torque (NT) mode of the dynamometer-engine control. The results show that diesel-CNG dual fuel (DDF) has better performance in terms of power, brake thermal efficiency, volumetric efficiency (VE), and exhaust temperature, making it suitable for commercial usage. While for regulated mass emissions like carbon monoxide (CO), total hydrocarbon (THC), and NOx, though DDF has shown higher emission compared to normal diesel, certain CNG flow rates were within the Euro 4 emission limit. Based on different criteria including engine performance and emissions, a matrix of CNG flow rates between 0.65 kg/hr and 3.0 kg/hr suitable for different loads and speeds has been optimized for the diesel engine.