GC-MS Speciation and Quantification of 1,3 Butadiene and Other C1-C6 Hydrocarbons in SI / HCCI V6 Engine Exhaust

It is known that the levels of hydrocarbon (HC) emissions from Homogeneous Charge Compression Ignition (HCCI) engines are relatively higher than that of Spark-Ignition (SI) engines because of the lower combustion temperature. In order to improve understanding of the mechanisms and products of HCCI combustion in comparison with SI combustion, a quantitative analysis of individual hydrocarbons in the C₁ - C₆ range emitted in the exhaust gases of gasoline direct injection V6 engine operating in SI and HCCI modes with cam profile switching has been carried out using gas chromatography - mass spectrometry (GCMS) apparatus attached on-line to engine exhaust. In this study, with a GC run time of 20 minutes all aliphatic and olefinic hydrocarbon species in the range C₁ to C₆ are resolved. It is shown that typical 1,3-Butadiene levels in the exhaust of engine operating in SI mode were in range of 9 to 32 μg/g (ppm) for different operation conditions, whereas in contrast, the exhaust from the same engine speed and load in HCCI mode contained almost no 1,3-Butadiene. The common exhaust products of this engine in the two different modes are Methane, Ethylene, Propylene, n-Butane, 1-pentene and n-Hexane at different levels. The total contribution of the lighter species remained practically unaltered when the engine operating parameters were varied, though their individual concentrations did change. The contribution of heavier hydrocarbons (over C₆) attributed to unburned fuel was determined under the same operation condition in the two different combustion modes. The results have shown that the hydrocarbon compounds in range of (C₆ - C₁₂) are responsible for most of hydrocarbon emissions, 50 - 70 % in case of SI mode and 69 - 88 % in case of HCCI mode using the same gasoline fuel and speed/load conditions.