Michael Mosburger

Graduate Student Research Assistant

Carbon Monoxide Diagnostics

To boost fuel efficiency and lower the emission of toxic gases of modern internal combustion engines, primarily two main improvements over common combustion strategies are available:

Spray-guided direct injection allows for globally very lean air/fuel ratios. The fuel is stratified to ideally form a cloud of stoichiometric air/fuel ratio right around the spark plug to ensure a good start of combustion by spark-ignition. The major advantage comes from the fact that a throttle plate in the intake manifold is no longer necessary to control engine load. Excess air is simply kept around the fuel cloud and emitted with the exhaust. Because the engine does no longer get chocked under low load operating condition, fuel efficiency can be improved significantly.

So-called Homogeneous Charged Compression Ignition (HCCI) is another highly interesting idea to increase fuel efficiency and lower emissions. The global air/fuel ratios are still kept lean and the throttle plate is no longer needed. But unlike in stratified direct injection the fuel is distributed equally over the entire combustion chamber. Because of the very lean air/fuel ratio, the combustion can no longer be initiated by a spark. Therefore, the compression is increased to initiate self-ignition of the fuel similar to the ignition process in a Diesel engine.

Both concepts suffer from a common problem though. Under certain operating conditions the emission of carbon monoxide (CO) is significantly higher. While it is of course possible to clean the exhaust in a catalytic converter further down in the exhaust stream, it is desirable to avoid CO emission in the first place for various reasons.

CO is also a very interesting molecule for the combustion of hydrocarbon fuels in general, besides the aforementioned problematic CO emission. It was found that CO plays a very important role in generating the main heat release in hydrocarbon flames. To better understand the combustion process itself and to validate combustion models, it is desirable to actually measure the CO concentration at different points in time during the combustion event and at different locations in the combustion chamber.

I am trying to develop a measurement technique that will allow for carbon monoxide diagnostics in the flame of an internal combustion engine during the combustion event. My approach utilizes Laser Induced Fluorescence (LIF) to first excite the CO with a laser beam and subsequently record the fluorescence light from the CO molecule. This approach will allow for measurements with both high spatial and temporal resolution. The focus of this research lies on designing the diagnostics tool such that it also allows for quantifying the absolute concentration of CO in the combustion gas. In order to do so, very fundamental knowledge has first to be generated about the excitation and fluorescence properties of CO under a wide temperature and pressure range as we see them in typical combustion events.