Experimental and numerical investigation of the effects of adding water to the intake air on engine performance, combustion and exhaust emissions in diesel engines

In this study, the effect of the water addition into the intake air (WAIA) on engine performance, combustion and exhaust emissions in diesel engines have been investigated experimentally and numerically. In the experimental study, different ratios of WAIA have been studied in an automotive diesel engine under different loads and engine speeds. It is determined from experimental results that brake specific fuel consumption (BSFC) generally decreases at 2000 rpm, but BSFC increases at 4000 rpm for selected water ratios (WRs). Also, WAIA reduces nitrogen oxides (NOx) emissions significantly at all speeds. Besides, WAIA generally increases cylinder pressures, but it mostly decreases cylinder temperatures, heat release rates (HRR) and combustion durations (CDs). Also, an empirical correlation has been developed for estimating CDs using the experimentally HRR values. In the numerical study, Ferguson's thermodynamic model has been used and adapted with new assumptions to compute the diesel engine cycle. Firstly, the reliability of the model for NDF and WAIA has been controlled by comparing the experimental and numerical results with that of studies in the literature. The model has been applied in the test engine at untested 2250 rpm and (5 and 7.5) % WRs condition. It has been found that the effective power (EP) decreases, the BSFC increases and NOx emissions significantly decrease for these WRs. Also, the model has been applied to a diesel engine, which is used in 2021 Renault Talisman, for (3, 6 and 9) % WRs at 4000 rpm. It is determined that for (3-6) % WRs, EP increase, and NOx emissions reduce significantly without much deterioration in the BSFC at 4000 rpm. Key Words: Diesel engine, Thermodynamic model, Water addition into the intake air, Heat release rate, Combustion duration, NO emissions