Michael Lammert

Effect of B20 and Low Aromatic Diesel on Transit Bus NOx Emissions Over Driving Cycles with a Range of Kinetic Intensity

This research project compares the emissions of oxides of nitrogen (NOx) from transit buses on as many as five different fuels and three standard transit duty cycles. The objective of the project is to establish if there is a real-world biodiesel NOx increase for transit bus duty cycles and engine calibrations. Prior studies have shown that biodiesel, sometimes called B20, can cause a small but significant increase in NOx emissions for some engines and duty cycles. Six buses that span engine build years from 1998 to 2011 were tested on the National Renewable Energy Laboratorys (NREL) Renewable Fuels and Lubricants (ReFUEL) research laboratorys heavy-duty chassis dynamometer with certification diesel, certification B20 blend, low aromatic California Air Resources Board (CARB) diesel, low aromatic B20 blend, and B100 fuels over the Manhattan, Orange County and the Urban Dynamometer Driving Schedule (UDDS) test cycles. The buses that were selected did represent a majority of the current national transit fleet. The selected buses also included hybrid and selective catalyst reduction (SCR) systems that are increasing in numbers in current transit vehicle fleets. The kinetic intensity of the tested duty cycle being the secondary driving factor, the engine emissions certification level had the dominant effect on NOx. With the exception of the 2008 model year bus, the biodiesel effect on NOx emissions was not statistically significant for most buses and duty cycles for blends with certification diesel. CARB fuel had many more instances of a statistically significant effect of biodiesel by substantially increasing NOx. SCR systems proved effective at reducing NOx emissions to near the detection limit on all duty cycles and fuels, including B100. A hybrid system proved to significantly increase NOx emissions over a same model year bus with a conventional drivetrain and the same engine. Because all but one test bus were equipped with diesel particulate filter after-treatment, particulate matter (PM) emissions were negligible and trends could not be drawn. On the oldest sample bus without after-treatment, PM emissions were reduced with B20 blends. The project shows how fuel economy was not significantly changed by the engine certification level, except that the 2008 conventional bus had the best performance on all cycles while all other buses had very similar results on each cycle. All buses had lower fuel economy with increased kinetic intensity of the cycle.

Influences on Energy Savings of Heavy Trucks Using Cooperative Adaptive Cruise Control

An integrated adaptive cruise control (ACC) and cooperative ACC (CACC) was implemented and tested on three heavy-duty tractor-trailer trucks on a closed test track. The first truck was always in ACC mode, and the followers were in CACC mode using wireless vehicle-vehicle communication to augment their radar sensor data to enable safe and accurate vehicle following at short gaps. The fuel consumption for each truck in the CACC string was measured using the SAE J1321 procedure while travelling at 65 mph and loaded to a gross weight of 65,000 lb, demonstrating the effects of: inter-vehicle gaps (ranging from 3.0 s or 87 m to 0.14 s or 4 m, covering a much wider range than previously reported tests), cut-in and cut-out maneuvers by other vehicles, speed variations, the use of mismatched vehicles (standard trailers mixed with aerodynamic trailers with boat tails and side skirts), and the presence of a passenger vehicle ahead of the platoon. The results showed that energy savings generally increased in a non-linear fashion as the gap was reduced. The middle truck saved the most fuel at gaps shorter than 12 m and the trailing truck saved the most at longer gaps, while lead truck saved the least at all gaps. The cut-in and cut-out maneuvers had only a marginal effect on fuel consumption even when repeated every two miles. The presence of passenger-vehicle traffic had a measurable impact. The fuel-consumption savings on the curves was less than on the straight sections.

Field Evaluation of Biodiesel (B20) Use by Transit Buses

The objective of this research project was to compare B20 (20% biodiesel fuel) and ultra-low-sulfur (ULSD) diesel-fueled buses in terms of fuel economy, vehicle maintenance, engine performance, component wear, and lube oil performance. We examined 15 model year (MY) 2002 Gillig 40-foot transit buses equipped with MY 2002 Cummins ISM engines. The engines met 2004 U.S. emission standards and employed exhaust gas recirculation (EGR). For 18 months, eight of these buses operated exclusively on B20 and seven operated exclusively on ULSD. The B20 and ULSD study groups operated from different depots of the St. Louis (Missouri) Metro, with bus routes matched for duty cycle parity. The B20and ULSD-fueled buses exhibited comparable fuel economy, reliability (as measured by miles between road calls), and total maintenance costs. Engine and fuel system maintenance costs were also the same for the two groups after correcting for the higher average mileage of the B20 group. Fuel filter plugging during unseasonably cold temperatures was more prevalent for the B20 group. Lube oil samples were collected over a wide range of mileage within the drain interval, and analyses indicate reductions in soot loading and wear metals in the B20 buses. Viscosity loss and lead corrosion were greater in the B20 group, while the total base number (TBN) loss was not significantly changed.

Exploring Telematics Big Data for Truck Platooning Opportunities

NREL completed a temporal and geospatial analysis of telematics data to estimate the fraction of platoonable miles traveled by class 8 tractor trailers currently in operation. This paper discusses the value and limitations of very large but low time-resolution data sets, and the fuel consumption reduction opportunities from large scale adoption of platooning technology for class 8 highway vehicles in the US based on telematics data. The telematics data set consist of about 57,000 unique vehicles traveling over 210 million miles combined during a two-week period. 75% of the total fuel consumption result from vehicles operating in top gear, suggesting heavy highway utilization. The data is at a one-hour resolution, resulting in a significant fraction of data be uncategorizable, yet significant value can still be extracted from the remaining data. Multiple analysis methods to estimate platoonable miles are discussed. Results indicate that 63% of total miles driven at known hourly-average speeds happens at speeds amenable to platooning. When also considering availability of nearby partner vehicles, results indicate 55.7% of all classifiable miles driven were platoonable. Analysis also address the availability of numerous partners enabling platoons greater than 2 trucks and the percentage of trucks that would be required to be equipped with platooning equipment to realize more than 50% of the possible savings.

Potentials for Platooning in U.S. Highway Freight Transport

Smart technologies enabling connection among vehicles and between vehicles and infrastructure as well as vehicle automation to assist human operators are receiving significant attention as a means for improving road transportation systems by reducing fuel consumption – and related emissions – while also providing additional benefits through improving overall traffic safety and efficiency. For truck applications, which are currently responsible for nearly three-quarters of the total U.S. freight energy use and greenhouse gas (GHG) emissions, platooning has been identified as an early feature for connected and automated vehicles (CAVs) that could provide significant fuel savings and improved traffic safety and efficiency without radical design or technology changes compared to existing vehicles. A statistical analysis was performed based on a large collection of real-world U.S. truck usage data to estimate the fraction of total miles that are technically suitable for platooning. In particular, our analysis focuses on estimating “platoonable” mileage based on overall highway vehicle use and prolonged high-velocity traveling, and established that about 65% of the total miles driven by combination trucks from this data sample could be driven in platoon formation, leading to a 4% reduction in total truck fuel consumption. This technical potential for “platoonable” miles in the United States provides an upper bound for scenario analysis considering fleet willingness and convenience to platoon as an estimate of overall benefits of early adoption of connected and automated vehicle technologies. A benefit analysis is proposed to assess the overall potential for energy savings and emissions mitigation by widespread implementation of highway platooning for trucks.