Calculation of mass emissions, oxygen mass fraction and thermal capacity of the inducted charge in SI and diesel engines from exhaust and intake gas analysis

摘要

New computational procedures are proposed for experimentally evaluating air-fuel ratio and mass fractions of exhaust emissions as well as ECR rate, oxygen mass fraction and thermal capacity of the inducted charge in IC engines running with diesel oil, gasoline or any alternative liquid or gaseous fuel, such as LPG or CNG. Starting from the chemical reaction of fuel with air, from gaseous and smoke level measurements in the raw gases, the procedures calculate the volume fractions of oxygen in the combustion air and of compounds in the exhaust gases, including those that are not usually measured, such as water, nitrogen and hydrogen. The methods also take the effects of various fuel and combustion air compositions into account, as well as to the presence of water vapor, CO_2, Ar and He in the combustion air. The algorithms are applied to four different automotive engines under wide ranges of steady-state operating conditions: three turbocharged diesel engines featuring high-pressure cooled ECR systems, and an SI naturally aspirated bi-fuel engine running on either gasoline or CNG. The computed air-fuel ratios are compared to those obtained from directly measured air and fuel mass-flow rates as well as from more conventional UEGO sensor data. The mass emissions are worked out in terms of both brake specific mass emissions and emission indexes of each pollutant species, and the results are compared to those obtained by applying SAE and ISO recommended practices. The computed oxygen mass fraction of the inducted charge was then compared to that derived from direct measurement of O_2 concentration in inlet manifold. Finally, the sensitivity of results to the main engine working parameters, the influence of environmental conditions (in particular the effect of air humidity on NO_x formation) and the experimental uncertainties are determined.