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A tri-generation cycle consisting of a homogeneous charge compression ignition (HCCI) engine and an ammonia-water absorption cogeneration cycle are proposed and analyzed. The energy of engine exhaust gases are utilized to run absorption cogeneration cycle. Also the energy of cooling water can be used in residential applications. A single zone model with capability to consider chemical kinetic talculations is developed for the HCCI engine. The results show that increasing the pump pressure ratio of the cogeneration cycle causes a decrease in the refrigeration output and an increase in first law efficiency. At a particular value of this pressure ratio the second law efficiency is maximized. It is shown that the contribution of engine in the total exergy destruction in the tri-generation system is much higher than those of the other components. With an ammonia concentration of 0.4 in the solution leaving the absorber and with an ambient temperature of 25oC, the maximum exergy efficiency occurs when the pump pressure ratio is 9.486. At this condition, the fuel energy saving ratio and CO2 emission reduction are 27.97% and 4.8%, respectively. It is also shown that the second law efficiency of the tri-generation system is 5.4% higher than the second law efficiency of the HCCI engine.

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Homogeneous charge compression ignition (HCCI) has attracted lots of attention due to the high thermal efficiency, lower NO­_x, and Soot exhaust emissions. Heat transfer from the gases to the combustion chamber walls has effective impact on the combustion process and the formation of engine-out emissions in HCCI engine. In this study for the first time a zero-dimensional single-zone model coupled with detailed chemical kinetics was used to evaluate the semi-empirical heat transfer models of Annand, Woschni, Hohenberg along with Assanis and Hensel to calculate heat flux in an HCCI engine fueled with natural gas. For this purpose, the 3D-CFD model coupled with detailed chemical kinetics was firstly validated by using experimental data, and then the 3D derived model was used as a base model for evaluating zero-dimensional model. Furthermore, the response surface model (RSM) was employed for investigating the effect of input parameters of engine including intake pressure (1, 1.25, and 1.5bar), equivalence ratio (0.3, 0.5, and 0.7), and engine speed (800, 1100, and 1400rpm) on the output parameters i.e., in-cylinder pressure and heat flux. In most cases were assessed, the zero-dimensional simulation results indicated that Annand technique provided the best model for heat flux simulation. Besides, the model of Hohenberg overpredict the heat flux in comparison with the calculated values derived from the 3D model, while Assanis and Hensel models underpredict the heat flux compared with the evaluated value of the 3D model. Furthermore, Woschni’s model cannot be used to model the heat flux in HCCI engine.