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Natural Gas engines are viewed as an alternative to diesel power in the quest to reduce heavy duty vehicle emissions in polluted urban areas. In particular, it is acknowledged that natural gas has the potential to reduce the inventory of particulate matter, and this has encouraged the use of natural gas engines in transit bus applications. Extensive data on natural gas and diesel bus emissions have been gathered using two Transportable Heavy Duty Vehicle Emissions Testing Laboratories, that employ chassis dynamometers to simulate bus inertia and road load. Most of the natural gas buses tested prior to 1997 were powered by Cummins L-10 engines, which were lean-burn and employed a mechanical mixer for fuel introduction. The Central Business District (CBD) cycle was used as the test schedule.

In order to obtain meaningful analyses of exhaust gas emissions and fuel economy for a heavy duty vehicle from a chassis dynamometer, the accurate simulation of road load characteristics is crucial. The adjusted amount of power to be absorbed by the chassis dynamometer during road driving of the tested vehicle needs to be calculated. In this paper, the performance of the chassis dynamometer under transient load cycle operations is discussed and the transient response of the power absorption system is presented. In addition, the design criteria of the chassis dynamometer used to test heavy duty vehicles under steady and transient load is described.

The federal emission standards for heavy duty vehicle engines require the exhaust emissions to be measured and calculated in unit form as grams per break horse-power-hour (g/bhp-hr). Correct emission results not only depend on the precise emission measurement but also rely on the correct determination of vehicle energy consumption. A Transportable Heavy-Duty Vehicle Emission Testing Laboratory (THDVETL) designed and constructed at West Virginia University provides accurate vehicle emissions measurements in grams over a test cycle. This paper contributes a method for measuring the energy consumption (bhp-hr) over the test cycle by a chassis dynamometer. Comparisons of analytical and experimental results show that an acceptable agreement is reached and that the THDVETL provides accurate responses as the vehicle is operated under transient loads and speeds. This testing laboratory will have particular value in comparing the behavior of vehicles operating on alternative fuels.

Concern over dwindling oil supplies has led to the adoption of alternate fuels to power fleet vehicles. However, during the interim period when alternate fuel supply stations are few and far between, dual fuel engines prove a necessity. In the light duty arena, these engines are typically gasoline engines modified to accommodate compressed natural gas (CNG) as an alternate fuel, but they are seldom optimized with both fuels in mind. A Saturn 1.9 liter 4 cylinder dual overhead cam engine was selected as a base for developing an optimized gasoline/CNG powerplant. Baseline data on power and steady state emissions (CO2, CO, NOx, HC) were found using the standard Saturn controller. In addition to monitoring standard sensor measurements, real-time pressure traces were taken for up to 256 cycles using a modified head with embedded PCB piezoelectric pressure transducers.

Concern over atmospheric pollution has led to the development of testing procedures to evaluate the hydrocarbon, carbon dioxide, carbon monoxide and oxides of nitrogen emissions from internal combustion engines. In order to perform emissions testing on vehicles, a chassis dynamometer capable of simulating expected driving conditions must be employed. West Virginia University has developed a Heavy Duty Transportable Emissions Testing Laboratory to perform chassis testing on trucks and buses. Emissions from the vehicle are monitored and recorded over the duration of a testing schedule. Usually the vehicle emissions from the whole test are reported as mass of emissions per unit distance driven. However, there is interest in relating the instantaneous emissions to the immediate conditions at specific points in the test, and in determining the emissions for discrete segments of the test (modal analysis).

Emissions from light duty vehicles have traditionally been measured using a chassis dynamometer, while heavy duty testing has been based on engine dynamometers. However, the need for in-use vehicle emissions data has led to the development of two transportable heavy duty chassis dynamometers capable of testing buses and heavy trucks. A test cycle has been developed for Class 8 trucks, which typically have unsyncronized transmissions. This test cycle has five peaks, each consisting of an acceleration, cruise period, and deceleration, with speeds and acceleration requirements that can be met by virtually all vehicles in common service. Termed the “WVU 5 peak truck test”, this 8 km (5 mile) cycle has been used to evaluate the emissions from diesel and ethanol powered over-the-road tractors and from diesel and ethanol powered snow plows, all with Detroit Diesel 6V92 engines.

Techniques have been developed to sample and speciate dilute heavy duty diesel exhaust to determine the specific reactivities and the ozone forming potential. While the Auto/Oil Air Quality Improvement Research Program (AQIRP) has conducted a comprehensive investigation to develop data on potential improvements in vehicle emissions and air quality from reformulated gasoline and various other alternative fuels. However, the development of sampling protocols and speciation of heavy duty diesel exhaust is still in its infancy [1, 2, 3, 4, 5 and 6]. This paper focuses on the first phase of the heavy duty diesel speciation program, that involves the development of a unique set of sampling protocols for the gas phase, semi-volatile and particulate matter from the exhaust of engines operating on different types of diesel fuel. Effects of sampling trains, sampling temperatures, semi-volatile adsorbents and driving cycles are being investigated.

Data has been gathered using the West Virginia University Heavy Duty Transportable Emissions Laboratories from buses operating on diesel and a variety of alternate fuels in the field. Typically, the transportable chassis dynamo meter is set up at a local transit agency and the selected buses are tested using the fuel in the vehicle at the time of the test. The dynamometer may be set up to operate indoors or outdoors depending on the space available at the site. Samples of the fuels being used at the site are collected and sent to the laboratory for analysis and this information is then sent together with emissions data to the Alternate Fuels Data Center at the National Renewable Energy Laboratory. Emissions data are acquired from buses using the Central Business District cycle reported in SAE Standard J1376; this cycle has 14 ramps with 20 mph (32.2 km/h) peaks, separated by idle periods.

This paper presents results from a study on speciation of the emission profiles and on the ozone forming potential of heavy-duty diesel exhaust under steady state engine operation. Very limited attempts have been made at determining the ozone forming potential of heavy duty diesel exhaust emissions. In this study a proportional sample of the dilute exhaust was drawn from a CFV-CVS system using a temperature controlled sampling line. The particulate matter was collected on a 70 mm Teflon coated glass fiber filter (TX40HI20WW), the semi-volatiles on XAD-2 copolymer resin and volatiles in Tedlar bags. The samples were analyzed by gas chromatography after conditioning and chemical extractions. The initial phase of the study was directed towards developing techniques and establishing protocols to determine the ozone forming potential of heavy-duty diesel exhaust. A pre-chamber naturally aspirated engine was tested on steady-state modes 1, 3, 5, 7 and 8 of the ISO 8 mode cycle.

Synthetic diesel fuel can be made from a variety of feedstocks, including coal, natural gas and biomass. Synthetic diesel fuels can have very low sulfur and aromatic content, and excellent autoignition characteristics. Moreover, synthetic diesel fuels may also be economically competitive with California diesel fuel if produced in large volumes. Previous engine laboratory and field tests using a heavy-duty chassis dynamometer indicate that synthetic diesel fuel made using the Fischer-Tropsch (F-T) catalytic conversion process is a promising alternative fuel because it can be used in unmodified diesel engines, and can reduce exhaust emissions substantially. The objective of this study was a preliminary assessment of the emissions from older model transit operated on Mossgas synthetic diesel fuel. The study compared emissions from transit buses operating on Federal no. 2 Diesel fuel, Mossgas synthetic diesel (MGSD), and a 50/50 blend of the two fuels.

Emissions of six 32 passenger transit buses were characterized using one of the West Virginia University (WVU) Transportable Heavy Duty Emissions Testing Laboratories, and the fixed base chassis dynamometer at the Colorado Institute for Fuels and High Altitude Engine Research (CIFER). Three of the buses were powered with 1997 ISB 5.9 liter Cummins diesel engines, and three were powered with the 1997 5.9 liter Cummins natural gas (NG) counterpart. The NG engines were LEV certified. Objectives were to contrast the emissions performance of the diesel and NG units, and to compare results from the two laboratories. Both laboratories found that oxides of nitrogen and particulate matter (PM) emissions were substantially lower for the natural gas buses than for the diesel buses. It was observed that by varying the rapidity of pedal movement during accelerations in the Central Business District cycle (CBD), CO and PM emissions from the diesel buses could be varied by a factor of three or more.