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Real time individual hydrocarbon tailpipe emission monitoring on a ‘lambda one’ (stoichiometric air/fuel ratio, i.e. λ = 1) controlled vehicle, driven in the ‘Neuer Europäischer Fahrzyklus’ (NEFZ) driving cycle on the chassis dynamometer, showed dramatic variations in the concentrations of butadiene and benzene when operated with gasoline having different octane ratings. Butadiene and benzene emissions were higher in 91 octane (RON) fuels compared to 95 and 98 octane fuels. The aromatics content of RON 91 fuel was significantly lower and the concentration of benzene was equal to the RON 95 fuel. The measured emissions of total hydrocarbons (THC) cannot reflect these differences, whereas cold start behaviors as well as highway driving emissions are derived from the test program.

In the compression and combustion strokes different individual hydrocarbons are generated through a complex reaction chemistry and can be monitored by a rapid V&F multicomponent gas analyzer system. They give detailed information on the physical properties of an engine. Through all different reaction sequences of the combustion, surface quenching reactions leave a characteristic pattern of hydrocarbons in the exhaust gas. Toluene and xylene, for example, represent direct monitors for unburnt fuel, alkenes and alkines show thorough fuel decomposition, allowing a rapid combustion when the spark is ignited, whereas aldehydes indicate autoignition processes. Ratios of hydrocarbon concentrations describe engine parameters like fuel/air mixing properties, EGR characteristics, autoignition processes, and engine oil combustion. So an optimized engine performance can be set by the hydrocarbon pattern measured in the direct exhaust gas.