Experimental Investigation of the Effect of Direct Water Injection on Combustion, Knock, and Emissions for LPG-Diesel Dual-Fuel Engine

Abstract

Liquefied petroleum gas (LPG) fuel has a high octane number and high heating value. These features make LPG a rather convenient alternative fuel for spark-ignition engines. On the other hand, using only LPG in diesel engines is not possible due to its low cetane number. However, LPG and diesel can be used in dual-fuel mode, a method that does not require significant modifications in diesel engines. In LPG-diesel dual-fuel mode, nitrogen oxide (NOx) emissions and knock intensity increase due to the rises in cylinder pressure and temperature, depending on LPG combustion and heat release characteristics under high load conditions. In this study, direct water injection with an electronic control method was utilized to reduce NOx and knock intensity in an engine running on LPG-diesel dual-fuel mode under full load conditions. For using LPG in a dual-fuel engine operating under full load without causing any damage, it is determined that the most convenient LPG ratio is 30% at the maximum. The test results obtained using neat diesel fuel are referred to as the standard engine data and are used in the comparisons for better understanding the results obtained. Direct water injection was applied into the engine cylinder at various ratios. During experiments, the ratio of injected water mass to fuel mass consumed in a cycle is set to 60%, 80%, and 100%, respectively. Increases in pressure, temperature, knock intensity, hydrocarbon (HC), and NOx emissions were observed in dual-fuel mode and are presented in comparison with the standard engine data. Consequently, specific fuel consumption, smoke opacity, and CO2 values were significantly reduced. By applying direct water injection and using diesel-LPG dual fuel of 30% LPG, significant improvements in engine performance parameters resulted, and NOx emissions in the dual-fuel condition reduced to lower levels than the standard engine data. Moreover, using direct water injection in dual-fuel mode reduced the increase in the combustion rate of fuel, but this increased the knock intensity.