The Improvement Of Calculation Method Of Diesel Engine Exhaust Emissions And The Analysis Of Error Factors

Diesel engine is a widely used power machine, the exhaust emissions of which cause environmental pollution and are harmful to the health of human beings. Many strict limits for exhaust emissions from engine are enacted in all kinds of rules. The exact test and calculation of emissions from engine are all-important, which ensure a convincing evaluation of the exhaust emissions levels.The present study investigates the calculation method of exhaust emissions from diesel engine, analyzes the characteristics of emissions from different types of diesel engines and probes into the test errors.There are mainly two kinds of ways to get the exhaust flow of the diesel engine. One way is to measure the exhaust flow directly. The other way is to calculate the exhaust flow indirectly by measuring the inlet air flow and the fuel flow or the concentration of the emissions components and the fuel flow. The latter way usually adopts simple C balance method and general C-O balance method, which calculate the exhaust flow and the brake specific emissions by measuring the fuel contents, the fuel flow and the concentration of emissions components.The simple C balance method provided by the GB/T 8190.1-1999, ignoring the affection of H₂O vapor in the inlet air to the calculation of exhaust flow, is inapplicable for case of fuel without N, O contents. The general C-O balance method, ignoring the Ar, CO₂ in the inlet air, is of mistake. This thesis re-reasons out the ameliorative simple C balance method and general C-O balance method, improves the calculation precision theoretically, and enlarges the range of application.In the analysis of calculation example of MAN B&W 5S50 MC diesel engine, the N, O contents work on the calculation value of the theoretical air mass flow per kg fuel, the excess air coefficient and the exhaust mass flow in application of the simple C balance method. The Ar and CO₂ in the inlet air cause about 3% error in calculation of exhaust flow, which should not be ignored in using the general C-O balance method. The calculating results of the brake specific emissions got by using the simple C balance method tally well with the result by using the general C-0 balance method.In this study, brake specific exhaust emissions tests are conducted in certain V type marine diesel engine under different test modes and cycles, with obvious differences in results governed by rule. In exhaust emissions test and calculation of certain vehicular engine, the error analysis shows that the measuring errors of the fuel contents, the fuel flow, the power and the concentration of emissions components influence on the calculation of brake specific exhaust emissions.The calculation methods put forward in the present study work out the brake specific exhaust emissions from the diesel engine in an accurate way, which is of great significance to the exhaust emissions test and the research into the decrease of diesel engine emissions.