Typical Off-design Performances Of Internal Combustion Engine CHP System

Internal combustion engine CCHP (combined cooling, heating and power) system has a variety of applications and great potentialities at home and abroad. Supported by National Nature Science Foundation Project, Algebraically Explicit Analytical Solutions of Energy Utilization etc, the aim of this research is to investigate the key problem of integration in cogeneration, to investigate system special law of design and off-design performances.Based on existed internal combustion engine performances, the main design parameters of variable types of engines are presented and summarized. The design performances and economy for different cogeneration is also analyzed. It can be found that internal combustion engine CCHP system has higher economic exergy efficiency than CHP (combined heat and power) system due to the difficulty in refrigeration.ICE (Internal combustion engine) and its cogeneration often run under off-design conditions due to engine load and ambient environment. Based on experimental data in references, typical off-design performances of ICE are investigated, which can represent the general typical off-design characteristics rather than any specific engine type. It can be found that engine exhaust gas temperature and exhaust gas flow drops with part load; power efficiency increases first and then decreases.Combined with analytical off-design performances of ICE and single pressure HRSG with saturated/superheated steam, typical off-design performances of the cogeneration is derived. The approach temperature difference, relative steam production and superheated steam temperature decrease with the decrease of load. Total energy efficiency, equivalent exergy efficiency and economic exergy efficiency increase first and then decrease. There exists an optimum value, corresponding to ICE best efficiency operating condition. It is worth emphasizing the safety operation of HRSG when approach temperature difference is likely to be negative in low load condition with high design steam parameter and low ICE design exhaust gas temperature, where water in economizer will be evaporated.Compared with single shaft gas turbine cogeneration, approach temperature difference in internal combustion engine CHP system is likely to be negative, which is not mainly because internal combustion engine has a decreased flue gas flow as the decrease of load, but also the rapid decreasing of exhaust gas temperature. Besides, the influence of off-design performance of combined system has little difference between saturated steam system and superheated steam system.Moreover, internal combustion engine power output and efficiency decrease with the decrease of ambient pressure. As a result, approach temperature difference, relative steam production and superheated steam temperature have a rapid decrease while the combined system efficiencies decrease slightly. It is necessary to consider influence of ambient environment, especially the optimization of ICE performances under High-altitude hypobaric areas.