Study of the Variations in Cylinder-Exhaust-Gas Temperature Over Inlet Air and Operation-Input Parameters of Compression-Ignition Engines

Cylinder-exhaust-gas temperature (T_exh) of a turbocharged compression-ignition engine indicates the levels of engine thermal loading on cylinder and exhaust components, thermal efficiency performance, and engine exhaust emissions. In consideration that T_exh is affected by engine air inlet condition that primarily includes inlet air temperature (T_i) and pressure (p_i), this paper studies the variation (ΔT_exh) of T_exh over varying the engine inlet air parameters of compression-ignition engines. The study is to understand ΔT_exh with appropriate relations between the inlet parameters and T_exh being identified and simply modeled. The regarded effects on T_exh and ΔT_exh for both naturally aspirated and turbocharged engines of this type are analyzed and predicted. The results indicate that T_exh increases as T_i increases or p_i decreases. The rate of variation in ΔT_exh over varying T_i or pressure p_i is smaller in a turbocharged engine than that in a naturally aspirated engine, as reflected from the model and results of the analysis. The results also indicate, for instance, T_exh would increase approximately by ∼2 °C as T_i increases by 1 °C or increase by ∼35 °C as p_i decreases by 10⁻²MPa, as predicted for a typical high-power turbocharged diesel engine operating at a typical full-load condition. The design and operating parameters significant in influencing ΔT_exh along with varying T_i or p_i are studied in addition. These include the degree of engine cylinder compression, the level of intake manifold air temperature, the magnitude of intake air boost, and the quantity of cycle combustion thermal input. As those parameters change, the rate of variation in T_exh varies. For instance, the results indicate that the rate of ΔT_exh versus the inlet air parameters would increase as the quantity of cycle combustion thermal input becomes higher. With the understanding of ΔT_exh, the engine output performances of thermal loading, efficiency, and exhaust emissions, concerning engine operation at variable ambient temperature or pressure, can be understood and evaluated for the purpose of engine analysis, design, and optimization.