Khanjani, K., Deng, J., and Ordys, A., "Controlling Variable Coolant Temperature in Internal Combustion Engines and its Effects on Fuel Consumption," SAE Technical Paper 2014-32-0064, 2014, doi:10.4271/2014-32-0064.
Increasing the efficiency and durability of internal combustion engines is one of the major concerns of engineers in the development of modern road vehicles. Emission legislations are becoming intensively strict each year, forcing manufacturers to deploy sophisticated engine control strategies. The engine coolant temperature is conventionally controlled with mechanical elements such as wax-thermostat and belt-driven mechanical water-pump, which result in engine temperature fluctuations and delayed response to variable inputs.Variable coolant temperature is beneficial; it can decrease the hydrodynamic frictional losses of lubricated engine parts in light duty conditions. Moreover it improves performance and protects engine parts from thermal stresses and sealing failure in heavy duty conditions.In this paper the feasibility of controlling coolant temperature is examined in different driver demand conditions using electric flow-control valve replacing conventional thermostat. Urban, extra urban and highway cycles are tested on Honda insight 2003 (without the electric motor) from Advisor software vehicle simulator. The engine conditions, speed and load, in corresponding cycles have been derived and used as an input to Matlab Simulink model consisting of engine cooling components, table of optimized coolant temperature and Brake Specific Fuel Consumption calculation algorithms.We demonstrated that fuel consumption savings of more than 1% in urban and extra-urban cycles can be achieved, however fuel consumption in highway cycle show negligible advantage. The system responds quickly to cooling since there is an amount of cold water reserved in the radiator; however the response is delayed in warming trends.