Characterization of the composition and toxicity of particulate matter emissions from advanced heavy-duty natural gas engines

Heavy-duty natural gas engines compliant with the 2010 EPA emissions standards have a clear advantage over diesel engines in meeting regulations with minimal after-treatment configuration. Heavy-duty natural gas engines are largely promoted as a cleaner burning engine with respect to low PM mass emissions. However, lack of sufficient data and literature on the exhaust emissions from advanced natural gas engines and the potential adverse health effects has raised concern amongst regulatory agencies. Also, the ammonia emissions from three-way catalyst equipped heavy-duty natural gas engines could be a major contributor to the formation of secondary PM in the atmosphere.;This CARB funded study focuses primarily on characterizing the toxicity of the volatile fraction of PM from advanced heavy-duty natural gas engines. The objective of the study also includes characterizing the unregulated species of the exhaust together with number concentration and size distribution of ultrafine nanoparticle emissions. CNG fueled transit buses were tested on WVU\u27s heavy-duty chassis dynamometer in Stockton, CA. A wide array of sampling procedures was included to characterize the complete chemical composition of the exhaust. The toxicity analysis included three different assays a) DHBA b) DTT and c) alveolar macrophage ROS assay.;Results of the gas phase chemical speciation results reported all carbonyl, PAH and VOC emissions close to levels found in background or below the detection limits of the analytical method. Results of elemental analysis reported elements such as calcium, phosphorus, potassium, zinc, sulfur and magnesium are some of the metals that were found in significant concentration in the PM samples. The findings of the study directly relate lubrication oil as the single most dominant source to non-volatile fraction PM emissions in the tailpipe. Both DHBA and DTT assay correlated highly with mass of elements and metals such as zinc, iron and cobalt. The DTT assay resulted in high correlation with mass of copper, zinc, phosphorus and PAH with molecular weight less than 200. The findings of this study also reported the possible formation of non-volatile nucleation mode particles of 10 nm size range

Evaluation of exhaust after-treatment device effectiveness in reducing regulated and unregulated emissions from natural gas fueled heavy duty transit bus

The promulgation of the public transit fleet rule by the California Air Resources Board (CARB) in 2000, has given transit fleet operators the option of choosing the alternative fuel path in order to reduce their fleet average NOx and PM emissions. Natural gas being an abundant domestic fuel, has found its way as an economically and technologically feasible alternative fuel option. Many studies have shown the clean burning nature of natural gas with lower NOx and near zero Particulate Matter (PM) emissions from heavy duty natural gas vehicles. Though natural gas fueled vehicles emit lower NOx and PM than their diesel counterparts, the emissions of carbon monoxide (CO) and total hydrocarbons (THC) are higher. This necessitates the use of a suitable exhaust after-treatment device to attain complete emission benefits.;The objective of the study was to measure regulated and unregulated emissions from CNG fueled heavy-duty transit bus with and without the after-treatment device present. The study conducted in Riverside, California utilized two CNG fueled transit buses one from Riverside Transit Authority (RTA) and the other from Los Angeles County Metro Transit Authority (LACMTA). The study required the complete chemical speciation of exhaust from the RTA bus with and without the after-treatment device so as to evaluate the effectiveness of the after-treatment device in reducing both regulated and unregulated emissions. The buses were retrofitted with an oxidation catalytic converter manufactured by Engine Control Systems (ECS). The buses were tested on a heavy duty chassis dynamometer part of the West Virginia University Transportable Heavy Duty Vehicle Emissions Testing Laboratory (WVTHDVETL). The transit buses were exercised over a double length Orange County Transit Authority (OCTA) cycle to characterize its emission levels. The analysis of the unregulated sample, which included Poly Aromatic Hydrocarbons (PAH), aldehydes, Volatile Organic Compounds (VOC), metals and elemental/organic carbon was done by Desert Research Institute (DRI).;The results of the regulated emissions showed a 99% reduction in CO and 62% reduction in THC with the after-treatment device present. The unregulated speciation results showed 96% reduction in carbonyl compounds with formaldehyde being the major contributor, 46% reduction in PAH compounds, 60% reduction in nitro-PAH compounds and 93% reduction in VOC. There was an overall 27% increase in metal content in exhaust with the after-treatment device present. There was no effect on the organic carbon concentration with the after-treatment device present