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A portable remote sensing system capable of real-time detection of particulate emissions from heavy-duty vehicles is being developed. The remote sensing technique employs optical extinction to measure the concentration of the carbonaceous fraction of the particulate matter and the CO2 in the exhaust plumes from individual vehicles. From these two measurements, instantaneous emission indices giving the mass of soot emitted to the amount of fuel burned by the vehicle at the given operating condition can be computed. Two tests designed to characterize the accuracy of the technique were conducted: 1) measurements through an exhaust plume from a laboratory diesel using a sequence of steady-state operating conditions; and 2) measurements of transient emissions from full size diesel-powered buses whose emissions were simultaneously measured in a full-scale dilution tunnel. In both cases, the remote sensing measurements were in good agreement with those obtained by conventional methods.

Particulate emissions from heavy-duty buses were measured in real time under conditions encountered during the standard Central Business District (CBD) driving cycle. The buses tested were equipped with 1994 Detroit Diesel Engine Corporation 6V92-TA engines, and some included after treatment devices on the exhaust. Instantaneous, time-resolved measurements of CO2 and amorphous carbon concentrations were obtained using an optical extinction technique and compared to simultaneous results obtained using conventional dilution tunnel sampling methods. Good agreement was obtained between the real-time extinction measurements and the diluted CO2 and cycle-integrated filter measurements. The instantaneous measurements revealed that acceleration transients accounted for roughly 80% of the particulate mass emitted during the cycle but only about 45% of the fuel consumption.

A new real-time soot concentration measurement technique for engine exhaust flows is presented. The technique uses a pulsed laser to illuminate the soot particles, with subsequent detection of the incandescence from the particles. Results are presented which show the detection limit, dynamic range, and dependence on operating conditions (i.e. size distribution and particle composition). The main advantages of the technique are its ability to detect small concentrations of soot such as those which would be present in the new clean diesel engines, its ability to give time-resolved measurements during the exhaust stroke, and its relative insensitivity to variable operating conditions.

This paper summarizes the state-of-the-art of various alternative fuel technologies for heavy-duty transit applications and compares them to conventional and “ clean” diesel engines. Alternative powerplants considered include compressed natural gas (CNG), liquefied natural gas (LNG), methanol, ethanol, liquefied petroleum gas (LPG), hydrogen, and several electric technologies. The various technologies are ranked according to emissions, operating and capital costs, safety, development status, driveability, and long term fuel supply. A simple spreadsheet-based rating system is presented; it not only provides a versatile, semi-quantitative way to rank technologies using both quantitative and qualitative information, but also helps identify critical areas which limit implementation for a given application. An example is given for urban transit buses.