Hong Kong Experience in Retrofitting in-use Diesel Vehicles 2003-01-1391
To abate the diesel vehicle emissions, Hong Kong Environmental Protection Department (HKEPD) has implemented comprehensive control measures including retrofitting programs for the pre-1995 light and heavy-duty diesel vehicles. Local franchised bus companies also carried out their own catalyst-retrofitting program in recent years as part of their emission control measures.
Before launching the retrofitting programs, we carried out trials to investigate the application issues of exhaust after treatment technology under local operation conditions. Parameters such as diesel catalyst cell density, engine exhaust temperature, backpressure, diesel fuel sulphur content and in-use catalyst durability performance that form the key elements for retrofitting are studied. Also, the in-use catalyst monitoring performance by the use of carbon monoxide (CO) and hydrocarbon (HC) measurement at high idle and dynamometer testing is investigated. This paper presents the above findings during the trials with the buses and the pre-1995 heavy-duty diesels.
During the bus trial, the catalyst durability performance is evaluated by emission testing under the US Heavy Duty Transient Test Cycle. The result shows that the catalyst could achieve 37% PM, 18% CO and 33% HC reductions after two year of use.
In the trial of 59 heavy-duty vehicles, the catalyst durability performance was monitored by testing two sample catalysts that were used for about one year. The dynamometer transient emission test shows a reduction of 36% PM, 48% CO and 56% HC when retrofitted onto a 1991 Cummins 8.3 L engine. The in-use performance of diesel catalyst of the trial fleet was also assessed by monitoring HC and CO concentration at high idle, on-road and lug-down test. The high idle test indicates an average of 72% in CO and 36% HC reduction though the catalysts are working at a lower temperature as compared with the on-road and lug-down tests which show a reduction of over 80% CO.
Based upon the trial findings and in consultation with worldwide technology providers, a panel of international experts wrote the two Particulate Removal Device (PRD) functional specifications. One specification for the local vehicles that will use Ultra Low Sulphur Diesel whilst the other specification is for the cross boundary vehicles which will use diesel with sulphur content up to 2,000 ppm. The PRDs must achieve over 35% particulate reduction initially and by no less than 25% after 250,000 km of use for local vehicles. The PRDs for cross boundary vehicles must achieve 25% particulate removal though out its 250,000 km warranty period. This paper also details the PRD specifications.