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The improvement in engine design and control techniques implies a reexamination of the cooling system. The aim of this research is to reduce fuel consumption and to increase passenger compartment thermal comfort through a better control of coolant flow rates and temperature. Preliminary experimental investigations, presented in the first part, permitted the development of a new cooling system. This system, described hereafter, is based on an electric pump and an automatic water-valve controlling the coolant flow rate and regulating the temperature at the cylinder head output. Finally are presented the vehicle tests; these confirm the results explained in the preliminary section: fuel consumption reduction, mainly due to a higher average coolant temperature, improved passenger compartment comfort through a monitored higher temperature level.

With the increasing efficiency of D.I. Diesel engines, the heat power needed to warm the passengers compartment becomes too low during the warm-up period. So the temperature increase of oil and water may be accelerate. This paper is devoted to the understanding of the phenomena involved in this process and their modeling. A diesel engine enclosed in a calorimeter is mounted on a test bench and largely instrumented. From the recorded data, the instantaneous energy balance is set up for different running conditions. Some general trends may be pointed out. During the first minute, 50% of the fuel energy is absorbed by the heat capacity of the heavy metallic components. This part progressively decreases to the benefit of heat transferred to the coolant. Furthermore, for increasing distance from the combustion chamber in the block, the rate of temperature rise decreases. Concerning the oil temperature evolution, it lags behind the water one.