# Thermodynamic Analysis of In-Cylinder Steam Assist Technology within an Internal Combustion Engine
###### Abstract  
For the requirements of rigorous CO\({}_{2}\) and emissions regulations, steam assist technology is an effective method for thermal efficiency enhancement. However, few studies apply steam assist technology in modern internal combustion engines. Stimulated by its application prospects, the present study proposes a thermodynamic analysis on the in-cylinder steam assist technology. An ideal engine thermodynamic model combined with a heat exchanger model is established. Some critical parameters, such as steam injection temperature, injection pressure and intake pressure, are calculated under different steam injection masses. The thermal efficiency boundaries are also analyzed at different compression ratios to investigate the maximum potential thermal efficiency of the technology. The analysis shows that the in-cylinder steam-assisted cycle has the potential to increase engine efficiency considerably. Both steam injection temperature and injection mass improve thermal efficiency. Considering the energy trade-off relationship between steam and exhaust gas, the maximum gain in thermal efficiency achieved with the cycle is 14.5% at a compression ratio of 10. The optimum thermal efficiency can be increased from 54.0% to 59.71% by increasing the compression ratio from 10 to 16. The mechanism lies in the specific heat ratio enhancement from a thermodynamic perspective, which improves the thermal-heat conversion efficiency. The results provide considerable guidance for the future experimental and numerical studies of in-cylinder steam assist technology into modern engines. in-cylinder steam assist technology; waste heat recovery; thermal dynamic modelling; internal combustion engine +
Footnote †: journal: Applied Sciences  
providing an opportunity to maximize its benefits [6]. Obviously, ICEs will still play a vital role in the automotive industry for at least several decades. Therefore, the long-term aim of engine researchers and manufacturers has been simultaneously focused on lower fuel consumption and emissions. For the requirements of rigorous CO\({}_{2}\) and emissions regulations, feasible solutions are being developed for energy conservation and emission reduction, including high ignition energy, cooled EGR [7], high tumble ratio, long-stroke, ultra-lean combustion [8; 9], homogeneous charge compression ignition, over-expansion cycles (Miller and Atkinson) [10], ultra high-pressure injection [11] and so on. Among them, in-cylinder steam assist technology has been proposed in recent years. Based on the Internal Combustion Engine 4.0 proposed by the AVL Co. Ltd., (Graz, Austria) water injection and steam processes are essential to achieving thermal efficiencies above 50% [12]. Developed from water injection technology, in-cylinder steam assist technology recovers thermal energy from engine coolant and exhaust gases and optimizes the combustion and emission features of prototype engines. In addition, the problems of metal corrosion and lubricating oil emulsification caused by liquid water slipping through the cylinder walls can be avoided [13; 14]. The steam assist technology has drawn much attention in recent years, and various forms of it have been realized. [PERSON] and [PERSON] et al. [15; 16; 17; 18; 19] conducted a series of investigations into the steam assist technology, in which steam was introduced into the combustion chamber by an intake manifold injector. The results demonstrate a specific fuel consumption drop of >5.0% and a power output increase of 0.6-2.8%. When the steam is introduced into a cylinder during the compression stroke, the power output increases by 5.9% to 7.8% at full load, while the injection timing moves from \(-120^{\circ}\) to \(-30^{\circ}\) CA ATDC [20]. The steam assist technology was also applied to the control and optimization of the elevated combustion temperature in the engine with an oxy-fuel combustion mode [21; 22; 23; 24]. [PERSON] et al.