Internal combustion engines in road traffic convert only approx. 30-40 % of the energy supplied via the fuel into mechanical energy. The rest must be dissipated as heat energy via exhaust gas, coolant or convection at the surfaces. This creates different temperature zones in the engine, and the engine oil acts as another heat-transfer medium between them.
The exact acquisition of the heat flows using the media of oil, water and air is a challenge for the measuring technology. Using optimized measuring setups and process flows, we achieve highest precision and repeat accuracy in the heat balancing of internal combustion engines.
For the heat balance measurement at the internal combustion engine, the temperature of the coolant is acquired at the engine system interface for inlet and outlet as well as the mass flow. The same applies to the engine oil. Both liquids are conditioned and can now be varied as desired at every operating point. Determining the heat flow of both media requires an accuracy of measurement that goes beyond the regular extent. For this reason, specially developed measuring devices are employed to determine the temperature. For a complete balancing, the fuel consumption, exhaust-gas heat, effective performance and convection are determined.
The program maps created by stationary load points with variations of the coolant or oil temperature are the basis for dimensioning the cooling systems in which the engine is to be installed and for the simulation of any, even extreme driving conditions.
In combination with the engine process computation and the one-dimensional flow computation, models can be created that completely describe the thermal system of the engine. This renders the heat balance measurement an important tool for improving thermal management, minimizing friction and reducing fuel consumption.
A difficult situation concerning emissions, but also that of heat availability in the passenger compartment, are represented by the cold start and the warmup from low negative temperatures.
The FKFS equipped an engine test bench with a cold chamber to measure and optimize these operating states. The test sample can be conditioned to a starting temperature of down to -23 °C. A dynamic dynamometric brake enables the simulation of any startup, starting and driving profiles. While intake air and ambient air are maintained at the desired ambient conditions, only that amount of heat is drawn from the coolant via the heat exchanger that is necessary for a predefined realistic warmup of the engine.
The goal of this method is the development of warmup strategies and the optimization of safety and comfort with increasingly more efficient engines.
The combustion engine is, on the one hand, the most important heat source in the cooling circuit of a conventional vehicle; on the other hand, it reacts significantly to modifications to the cooling system via consumption, nitrogen oxide emissions or the tendency to knock. In models, therefore, it should be depicted with sufficient accuracy. The basis for this can be thermal balance measurements on the engine test bench or existing test vehicles from our virtual engine construction kit.
The internal heat flows between gas, structure, water and oil must be precisely integrated and calibrated in order to achieve good predictive properties. Here a well-designed measurement program for separating the mechanisms of action is just as helpful as our methodology for model calibration.
A calibrated model of the base engine enables a high-quality description of the feedback effects of the cooling circuit on the engine. Alternatively, the engine application can also be changed: for example, EGR (exhaust gas recirculation) strategies can be evaluated, or peak pressure or compression ratio increased. In the same way, design changes can be made predictively, such as inserting an integrated exhaust manifold. Or the heating up of the base engine during a cold start from -20°C can be examined.