Abstract
This paper presents the results for liquid water injection (WI) into a cylinder during the compression and expansion strokes of an internal combustion engine (ICE), with the aim of achieving an optimal in-cylinder pressure and improving power output using CFD simulation. Employing WI during the compression stroke at 80° of crank angle (CA) before top dead centre (bTDC) resulted in the reduction of compression work due to a reduction in peak compression pressure by a margin of about 2%. The decreased peak compression pressure also yielded the benefit of a decrease in NOx emission by a margin of 34% as well as the prevention of detonation. Using WI during the expansion stroke (after top dead centre–aTDC) revealed two stages of the in-cylinder pressure: the first stage involved a decrease in pressure by heat absorption, and the second stage involved an increase in the pressure as a result of an increase in the steam volume via expansion. For the case of water addition (WA 3.0%) and a water temperature of 100 °C, the percentage decrease of in-cylinder pressure was 2.7% during the first stage and a 2.5% pressure increase during the second stage. Water injection helped in reducing the energy losses resulting from the transfer of heat to the walls and exhaust gases. At 180° CA aTDC, the exhaust gas temperature decreased by 42 K, 89 K, and 136 K for WA 1.0, WA 2.0, and WA 3.0, respectively. Increasing the WI temperature to 200 °C resulted in a decrease of the in-cylinder pressure by 1.0% during the first stage, with an increase of approximately 4.0% in the second stage. The use of WI in both compression and expansion strokes resulted in a maximum increase of in-cylinder pressure of about 7%, demonstrating the potential of higher power output.
Highlights
In recent years, concerns over environmental pollution and energy balance has resulted in major interest in research regarding the optimal design of internal combustion engines (ICEs), especially automobile engines
The results demonstrated that engine performance, brake specific fuel consumption (BSFC), and CO and HC emissions of the fuel blends were better than those of pure gasoline for the test conditions considered
The results of a CFD simulation were carried out to investigate the effect of water addition (WA) on the in-cylinder pressure and facilitate higher power output
Summary
Concerns over environmental pollution and energy balance has resulted in major interest in research regarding the optimal design of internal combustion engines (ICEs), especially automobile engines. In one study [3], hydroxide and hydrogen were formed from the thermal-dissociation process of water at high temperature, which absorbed the heat during combustion This method is useful for controlling the peak in-cylinder temperature and for reducing unwanted emissions. This study involved the coupling of a traditional ICE cycle with the steam expansion cycle using steam injection into the expanding cylinder In this way, the engine thermal efficiency can be improved by 6.3% at 6000 r/min. Using the waste heat from the exhaust gas and engine coolant system to heat up the injected water, the theoretical thermal efficiency of the ICE reached 53% and 67% when the WI temperature was 120 ◦C and 200 ◦C, respectively. The effects of WI (for simulation cases) on in-cylinder pressure, heat transfer, NO emission, and other factors were examined and are discussed in this study
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