Method for determining fuel and engine oil comsumption using tunable diode laser spectroscopy

A method is provided for precisely and concurrently measuring dynamic engine oil consumption and fuel consumption within an internal combustion engine in an automotive environment on a real time basis. Nonradioactive tracer compounds, such as bromine or chlorine in the form of organic bromo- or chloro-compounds are added to the engine oil in small amounts. Upon complete combustion, the bromine or chlorine is converted into either hydrogen bromide or hydrogen chloride. A sample of the exhaust gases generated by the internal combustion engine and comprising the hydrogen bromide or hydrogen chloride is collected and maintained at a pressure where distinction between an absorption line of the tracer specie and the absorption lines of a related isotopic species is discernible. Monochromatic radiation is then transmitted through the gaseous sample at the frequency of an absorption line particular to the tracer specie. Because of the high spectral power density and spectral resolution of the preferred tunable diode lasers, tunable diode laser spectroscopy may be used to measure the amount of tracer isotope within the resultant HCl or HBr gases in the exhaust gases. Corresponding fuel consumption may also be determined from the CO2 in the exhaust gases by similar methods.