Browsing by Author "Hofeldt, David L."

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    Evaluation of Alternative Fuel Options for Heavy-Duty Transit Vehicles
    (1993-02) Hofeldt, David L.
    The purpose of this report is to present a critical assessment of the current state-of-the-art of alternative fuel technologies for heavy-duty transit vehicles. Fuels considered include compressed natural gas (CNG), liquefied natural gas (LNG), methanol, ethanol, liquefied petroleum gas (LPG), hydrogen, and several advanced battery and fuel cell technologies. For each fuel type, results from the recent literature are collected to allow comparison of the combustion methods, emissions, power output, fuel efficiency, range, refueling requirements, development status, safety aspects, and infrastructure requirements of various engine designs. Since many of the engines are under various stages of development, data for operation and maintenance costs are somewhat scarce; however, such information is provided when possible. Short descriptions of problems remaining to be solved are given, but detailed comparisons between technologies are withheld until the Discussion and Comparison section in order to avoid biasing the initial presentations. The economic implications of the various strategies are then discussed in relation to the technical performance. Since the viability of heavy-duty vehicle operation depends to large extent on future emissions standards as well as the widespread availability of the given fuel, current and proposed emissions standards are listed, along with trends in light-duty and stationary applications involving the various fuels. Most of the work to date has centered on conversion and/or optimization of existing engine designs to accommodate the new fuels rather than the development of completely new engine concepts. Estimates of the capital cost and fuel economy of the various designs have been made, and the feasibility of retrofits versus dedicated engines are presented. The latter is especially important when one considers that poorly optimized retrofits may result in substantially higher emissions and maintenance costs than the original engines. A relative cost/benefit scale is formulated and used to rate the technologies, and the importance of the relative weighting factors in determining the outcome is discussed.
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    LIDAR System for Area Sensing of Vehicle Emissions: Final Evaluation Report
    (Minnesota Department of Transportation, 1998-01) Hofeldt, David L.
    This report presents an assessment of the effectiveness of an elastic LIDAR system (wavelength of 1.06 um) for wide-area remote sensing of pollutant concentrations associated with particulate plumes near urban roadways. Traditional point-sampling instruments were also used to measure mass concentrations of particulate matter and carbon monoxide (CO) concentrations near the roadways. The size distribution of the particulate matter was also measured, and variations in the size-resolved particle concentrations were compared to the LIDAR signal. We found that the LIDAR signal was most sensitive to the concentration particles whose characteristic dimensions were slightly larger than the wavelength of the laser used, and that a relation exists between the two. Hence, when used at low elevations near roadways, the 1.06 um wavelength LIDAR system located plumes of particles whose aerodynamic diameters fell in the 1-5 um size range, and tracked changes in their concentrations. Particles in this size range lie primarily in the coarse size range of respirable aerosols, and are readily made airborne by vehicle-induced air motion and thermal drafts associated with pavement and vehicle exhaust. The bulk of this report summarizes the operating characteristics of the LIDAR system; issues regarding field deployment, including eye safety, reliability, and operator training; requirements for image display and interpretation; and correlations between the LIDAR signal, pollutant concentrations, and traffic. The influence of varying weather conditions, primarily wind speed, direction, and relative humidity, is discussed. Recommendations for further development are also given, including comments on the feasibility of fine particle LIDAR and species specific LIDARS. Firm conclusions regarding the air quality impacts associated with the operation of a portable traffic management system designed to minimize traffic congestion cannot be drawn at this time due to uncertainties associated with the effectiveness of the traffic management system and large variabilities introduced by varying weather and traffic conditions.