Corrosion Resistance of Valve Steels in Combustion Gases from Gasoline and Propane-Butane

The corrosion resistances of widely used X33CrNiMnN23-8, X50CrMnNiNbN21-9, X53CrMnNiN20-8 and X55CrMnNiN20-8 high-alloyed austenite valves steels in combustion engines have been compared. The comparison was performed on the basis of results of kinetic corrosion of the test steels in combustion gases from gasoline with 5% ethanol additive （v/v） and the combustion gases from propane-butane. The corrosion test was performed gravimetrically under thermal shock conditions by heating samples of the test steels from room temperature up to 1,173 K in exhaust gases from a combustion engine, and holding them at this temperature for 2 h and then cooling at room temperature for about 25 min. Then the same thermal shock was repeated and after every 10 to 20 such cycles the mass of the specimens was measured. This experiment simulated the working conditions of a highly thermal loaded exhaust valve in a spark ignited engine. The analysis performed shows that the corrosion resistances of X33CrNiMnN23-8 and X50CrMnNiNbN21-9 valve steels in an environment of combustion gases from propane-butane and in gases from gasoline with 5% ethanol additive （v/v） are comparable, whereas the corrosion resistance of X53CrMnNiN20-8 and X55CrMnNiN20-8 valve steels in an environment of combustion gases from propane-butane is slightly worse than in gases from gasoline with 5% ethanol additive （v/v）.

An approach for predicting the toxicity of smoke

The N-GAS model for predicting smoke toxicity has been proposed for many years by NIST.However,almost all the existing CFD software cannot accurately predict the toxicity of smoke using the model because of the absence of the toxic gas concentration of HCN,NO x,HCl and HBr.In this work,an approach for predicting fire smoke toxicity was developed and demonstrated.A detailed mechanism including these fire effluents was constructed firstly,and the subsequent generation of state relationship among fire effluents,mixture fraction and strain rate was conducted by using opposed-flow flame technique.A mixture fraction-based combustion model used in FDS code was modified,and meanwhile the scalar dissipation rate transport equation was numerically solved.Thus the concentration of fire effluents as the function of mixture fraction and scalar dissipation rate can be calculated through a look-up table,and the toxic potency based on the 7-gas model can be obtained.The method was applied into an underground commercial street in Chongqing.It showed that the results between the 7-gas model and 3-gas model(CO,CO 2,and O 2) were obviously different.It indicated that there needs some modifications in conclusions and results from 3-gas model for fire-risk assessments.