A Critique on the Research Activities and Potential Benefits of Dual-Fuel Diesel Engines Run on Biogas and Oxygenated Liquid Fuels

The dual fuel concept of diesel engines is gaining popularity because of their ability to use alternative renewable gaseous fuels (natural gas, biogas, producer gas) and liquid fuels (biodiesel, alcohol, and others) simultaneously. The dual fuel mode (DFM) not only reduces the consumption of diesel or substitutes the diesel fuel, but there is an advantage of operating the engine in pure diesel mode (PDM) in case of shortage of gaseous primary fuel. The uses of renewable fuels in such engines have the positive impact on green ecosystem in terms of reduction in NOx and smoke emissions; however, there is the engine derating as performance penalty in comparison to engines operating under PDM. The most influential parameters in DFM engines are the type and flow rate of inducted gaseous fuel, fuel-air equivalence ratio (Phi(global)), compression ratio (CR), and injection timing (IT). During the last few decades, the researchers have studied the effect of various parameters to improve the overall performance characteristics (performance, combustion, and emission) of DFM engines. This paper makes an in-depth analysis to unveil the physical characteristics of the crucial parameters of DFM engines with specific reference to the use of biogas with ternary blends (TB) of diesel, biodiesel, and ethanol. The paper addresses the issues on how the gaseous fuel flow rate, preheating of the intake charge, compression ratio, injection timing, and the type of oxygenated fuels dominate the overall performance characteristics.