Subject Top Page: ARB CNG and Diesel Transit Bus Emissions Research

This page updated October 14, 2005.


CARB's Study of Emissions from In-Use CNG and Diesel Transit Buses

The Air Resources Board (ARB) has led a multi-agency research effort to collect emissions data from late-model heavy-duty transit buses in five different configurations. The objectives of the study were 1) to assess driving cycle effects, 2) to evaluate toxicity between new and "clean" heavy duty engine technologies in use in California, and 3) to investigate total PM and ultrafine particle emissions. Chassis dynamometer testing was conducted at ARB's Heavy-duty Emissions Testing Laboratory (HDETL) in Los Angeles. The impetus behind this work was to compare the emissions from transit buses powered by similar engines and fueled by ARCO (a BP company) Low Sulfur Emission Control Diesel (ECD-1) and compressed natural gas (CNG). Follow-on work focused on the assessment of aftertreatment control for CNG applications. Five vehicle configurations were investigated: 1) a CNG bus equipped with a 2000 DDC Series 50G engine certified for operation without an oxidation catalyst, 2) the same CNG bus retrofitted with an OEM oxidation catalyst, 3) a diesel bus equipped with a 1998 DDC Series 50 engine and a catalyzed muffler, 4) the same diesel vehicle retrofitted with a Johnson Matthey Continuously Regenerating Technology (CRT) diesel particulate filter (DPF) in place of the muffler, and 5) a CNG bus equipped with a 2001 Cummins Westport C Gas Plus engine and OEM-equipped oxidation catalyst. The duty cycles were: 1) idle operation, 2) a 55 mph steady-state (SS) cruise condition, 3) the Central Business District (CBD) cycle, 4) the Urban Dynamometer Driving Schedule (UDDS), and 5) the New York City Bus Cycle (NYBC). Collection of PM over multiple cycles was performed to ensure sufficient sample mass for subsequent chemical analyses. Information on regulated (NOx, HC's, PM, and CO) and non-regulated (CO₂, NO₂, gas-phase toxic HC's, carbonyl compounds, polycyclic aromatic hydrocarbons, elements, and elemental and organic carbon) emissions was collected. Size-resolved PM mass and number emission measurements were conducted and extracts from diesel and CNG total PM samples were tested in the Ames mutagenicity bioassay analysis to determine mutagen emission factors. An overview of results are reported below.


Overview of Results to Date

ARB Board Presentation, April 22, 2004	Presentation

CNG Oxidation Catalyst Evaluation
1) Chemical and bioassay analyses of emissions from two CNG buses with oxidation catalyst	Presentation
2) Partial Results: Emissions from two CNG buses with oxidation catalyst	Presentation	Briefing Paper

CNG and Diesel Comparison
1) ARB's study of emissions from late model diesel and CNG transit buses - toxic compounds and PM emissions	Presentation
2) ARB's study of emissions from late model diesel and CNG transit buses	Presentation

News Release "Air Board Tests Compare Diesel and CNG Bus Emissions"	News Release	Briefing Paper

Conference Presentations

List of Conference Presentations
16) 15th CRC On-Road Emissions Workshop Apr. 2005	Presentation
15) 14th CRC On-Road Emissions Workshop Apr. 2004	Poster
14) Chairman's Seminar Series Presentation	Presentation
13) American Association for Aerosol Research Oct. 2003	Presentation
12) Diesel Engine Emission Reduction Aug. 2003	Presentation	Paper
11) 7th ETH International Conference on Combustion Generated Particles Aug. 2003	Poster
10) 13th CRC On-Road Emissions Workshop Apr. 2003	Presentation
9) 13th CRC On-Road Emissions Workshop Apr. 2003	Presentation
8) CTA World Truck Conference March 2003	Presentation
7) Society of Automotive Engineers Nov. 2002	Presentation
6) American Association for Aerosol Research Oct. 2002	Presentation
5) American Public Transportation Association Sep. 2002	Presentation
4) Diesel Engine Emission Reduction Aug. 2002	Presentation
3) 6th ETH International Conference on Combustion Generated Particles Aug. 2002	Presentation
2) 12th CRC On-Road Emissions Workshop Apr. 2002	Presentation
1) 5th ETH International Conference on Combustion Generated Particles Aug. 2001	Presentation	Abstract

Papers

List of Papers
Environmental Science and Technology 2005-1	Paper
Environmental Science and Technology 2005-2	Paper
Environmental Science and Technology 2004 - Univ. of Conn.	Paper
SAE Technical Paper 2003	Paper
SAE Transactions Journal of Fuels and Lubricants 2002	Paper
Environmental Science and Technology 2002	Paper


*Other titles will be added as they become available.*




If you have questions or comments regarding the content on this web page, please contact Alberto Ayala at 916.327.2952 or via e-mail at aayala@arb.ca.gov



If you have questions or comments regarding this web page, please contact Steve Mara at 916.323.3920 or via e-mail at smara@arb.ca.gov

Research Activities

ARB CNG and Diesel Transit Bus Emissions Research

Resources

Program Links