Dynamic engine oil and fuel consumption measurements using tunable diode laser spectroscopy

In a method for evaluating fuel and engine oil consumption on a near real-time basis in an internal combustion engine, wherein the fuel or engine oil is treated with a nonradioactive tracer compound either in its natural isotopic abundance or enriched, the nonradioactive tracer compound being one or more compounds selected from the group consisting of organobromine compounds and organochlorine compounds, such that the exhaust gas of the internal combustion engine contains a tracer compound comprising a tracer isotopic specie;

• and wherein an exhaust gas sample continuously flows from the internal combustion engine through a sample cell in which the exhaust gas sample is maintained at a reduced pressure such that a distinction between an absorption line of the tracer isotopic specie and the absorption lines of related isotopic species is discernible;
• and wherein monochromatic radiation is transmitted through the exhaust gas sample in the sample cell at the frequency of an absorption line for the tracer isotopic specie, while concurrently detecting the intensity of a spectral line for the tracer isotopic specie, so as to determine fuel and engine oil consumption in the internal combustion engine on a near real-time basis;
• the improvement comprising the step of:
• continuously flowing the exhaust gas sample through a sample line in which the exhaust gas sample is rapidly expanded so as to attain the reduced pressure in the sample cell, and in which the exhaust gas sample is heated so as to substantially prevent water vapor present in the exhaust gas from condensing while the exhaust gas is at the reduced pressure, the sample line causing the dew point of the exhaust gas sample to be sufficiently low so as to allow the sample cell to be operated at approximately room temperature and so as to enable the tracer compound and the water vapor to coexist within the sample cell.