Gaseous and Particulate Emissions from a Waste Hauler Equipped with a Stoichiometric Natural Gas Engine on Different Fuel Compositions

We assessed gaseous and particulate matter (PM) emissions from a current technology stoichiometric natural gas waste hauler equipped with a 2011 model year 8.9L Cummins Westport ISL-G engine with cooled exhaust gas recirculation (EGR) and three-way catalyst (TWC). Testing was performed on five fuels with varying Wobbe and methane numbers over the William H. Martin Refuse Truck Cycle. The results showed lower nitrogen oxide (NO_x) emissions for the low methane fuels (i.e., natural gas fuels with a relatively low methane content) for the transport and curbside cycles. Total hydrocarbon (THC) and methane (CH₄) emissions did not show any consistent fuel trends. Non-methane hydrocarbon (NMHC) emissions showed a trend of higher emissions for the fuels containing higher levels of NMHCs. Carbon monoxide (CO) emissions showed a trend of higher emissions for the low methane fuels. The low methane fuels generally showed higher fuel economy on a volumetric basis compared to the higher methane number fuels. Carbon dioxide (CO₂) emissions did not show any statistically significant trends for either the transport or curbside cycles, but did show some reductions for some fuels for the compaction cycle. PM mass emissions were very low and there were no statistically significant differences between the fuels. Particle number emissions did not show strong fuel trends for the different RTC segments, with some exceptions. Results of the particle size distribution revealed bimodal size distribution profiles for all fuels, with a predominant nucleation mode centered from 9 to11 nm size range. Ammonia emissions showed a trend of higher emissions for the low methane fuels. Nitrous oxide (N₂O) emissions were higher with the low methane fuels. Formaldehyde emissions did not show any statistically significant fuel trends, while acetaldehyde emissions were at or below the background levels for most of the test fuels.