Measuring heat flux in internal combustion engines
Nitrogen oxides (NOx) produced inside vehicle engines are subsequently released to the atmosphere where they negatively impact human health. The pressure on automobile manufacturers is increasing as tighter vehicle emission standards are set to come into force. NOx formation in the combustion chamber is highly dependent on temperature. Therefore, attempts to re-engineer the Internal Combustion Engine (ICE) to reduce NOx emissions must be driven by knowledge of the temperature field. Unfortunately, detailed data for the various stages of the combustion cycle is lacking. Working under the auspices of the MINNOX project, the Universitaet Stuttgart constructed an innovative experimental set-up using special surface thermocouples. Using over 100 such sensors, the German engineers were able to obtain simultaneous measurements of the heat flux throughout the entire combustion chamber. This represents a quantum leap forward from past research efforts. The flexibility of the experimental apparatus facilitated the investigation of different intake geometries, flow field conditions and flame propagation. In addition, the low mass of the thermocouples enabled the collection of high-resolution data, on the order of one degree of Crank Angle (CA). In the context of the MINNOX project, the results of the Universitaet Stuttgart's research were used to calibrate three-dimensional engine simulation tools. Such tools will help vehicle manufacturers, such as those taking part in the project, advance engine technology more rapidly than previously possible. Finally, it should be noted that the experimental methodology can be applied to other engine components, such as fuel injectors.
