On the road measurements of pollutant gas emissions of two different CNG city buses

摘要

EEC Regulation R-49 for passenger vehicles does not porvide any indication on the emission levels of the vehicles under real conditions.For this reason,an on-the-road measuremetn method was developed.This mehtod was used to compare the pollutant gas emissions of four similar buses equipped with : a) a CNG engine with no catalytic converter (#lambda#=1.4); b) a CNG enginewith three way catalyst (#lambda#=1); c) standard diesel engine and d) a diesel enginecomplying with EUR-2 standards.the results showed acceptable consistency and,as expected,the CNG engine equipped with the three way catalyst was a low polluting engine,especially with respect to NO emissions (it emits from 1/3 to 1/5 as much as a standard diesel engine).However,its CO emission level was considerably higher,although a good dynamic control of the A/F ratio could greatly reduce this (a factor 3 or more is possible).