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As the demand for improved fuel economy increases and new CO2 regulations have been issued, aerodynamic drag reduction has become more critical. One of the important factors to consider is cooling drag. One way to reduce cooling drag is to decrease the air flow volume through the front grille, but this has an undesirable impact on cooling performance as well as component heat load in the under-hood area. For this reason, cooling drag reduction methods while keeping reliability, cooling performance and component heat management were investigated in this study. At first, air flow volume reduction at high speed was studied, where aerodynamic drag has the greatest influence. For vehicles sold in the USA, cooling specification tends to be determined based on low speed, while towing or driving up mountain roads, and therefore, there may be extra cooling capacity under high speed conditions.

In order to study the potentiality of the modification of the combustion rate for NOx formation control in the spark ignition (SI) engine, the authors first developed a new mathematical model by assuming the stepped gas temperature gradient in the cylinder. The predicted results from this new mathematical model show good coincidence with the experimental data. Second, the authors discuss the effects of the modification of the combustion rate on NOx formation using the new mathematical model. It was concluded that NOx formation in the premixed SI engine would be essentially determined by the specific fuel consumption only, regardless of any modification of the engine combustion rate.

It has been hitherto recognized merely by experience that the power output of a two-stroke cycle crankcase compression gasoline engine is inversely proportional to a power exponent larger than 0.5 of the absolute atmospheric temperature. To ascertain this effect, a 60 cm3 two-stroke cycle crankcase compression gasoline engine was performance tested at various inlet air temperatures. It was found that the power output varied inversely proportional to a power exponent ranging from 0.5 to 0.9 of the absolute inlet air temperature. This was explainable by the fact that the pressure ratio of the crankcase decreased as the air temperature increased and vice versa.