Energy Balance During the Warm-Up of a Diesel Engine

In the present work, an automotive Diesel engine has been experimentally tested under a New European Driving Cycle (NEDC) with the aim of getting experimental plots of time dependent partitioning of energy injected during the warm-up process. An additional objective of this work is to assess the energy recovery capacity installed in the engine, i.e., to assess how much of the energy that leaves the engine with the exhaust gasses and the coolant is being employed. With this target, mean values of some parameters (intake and exhaust pressures and temperatures, coolant flow and coolant inlet and outlet temperatures, engine speed and torque) together with instantaneous variables (crankshaft angle, in-cylinder gas pressure, intake and exhaust mass flows) were continuously recorded during the warm-up of the engine. As a result of the work, the dynamics of the thermal balance of the Diesel engine under transient road conditions during the warm-up period was obtained. Gross equivalent and detailed cumulative energy flows were measured. The driving cycle averaged values of exhaust gases and coolant energy rates make up 3.75 and 4.31 kW respectively in the engine tested. Thermal losses account for more than 30 % of the input energy, while the larger part of the input energy goes to the heating of engine masses during approximately the first third part of the NEDC cycle. For the urban parts of the cycle the mean value of exhaust gases temperature does not exceed 200°C, and the corresponding averaged energy rates are 2.84 and 2.18 kW for the exhaust gases and the coolant. The coolant temperature takes approximately 720 seconds to reach 80°C. The mean value of the sum of the energy recovered by the exhaust gas recirculation (EGR) cooler and the passenger cabin heater core is of the order 1.5 kW. The data obtained can be used to establish nominal design parameters for efficient waste energy recovery systems.