David Klinikowski

Development of a Dimethyl Ether (DME)-Fueled Shuttle Bus

Dimethyl Ether (DME) is a potential ultra-clean diesel fuel. Its unique characteristics require special handling and accommodation of its low viscosity and low lubricity. In this project, DME was blended with diesel fuelto provide sufficient viscosity and lubricity to permit operation of a 7.3 liter turbodiesel engine in a campus shuttle bus with minimal modification of the fuel injection system. A pressurized fuel delivery system was added to the existing common rail injection system on the engine, allowing the DME-diesel fuel blend to be circulated through the rail at pressures above 200 psig keeping the DME in the liquid state. Fuel exiting the rail is cooled by finned tubed heat exchangers and recirculated to the rail using a gear pump. A modified LPG tank (for use on recreational vehicles) stores the DME- diesel fuel blend onboard the shuttle bus. A small cylinder of helium is used to provide a blanket of inert gas above the fuel mixture to keep the DME in the liquid state and to push the mixture to the fuel rails. A significant challenge is posed by the rapid increase in DME vapor pressure with increasing fuel temperature. As the fuel mixture passes through the rail, it is heated by the surrounding surfaces in the cylinder head. The target for maximum fuel rail temperature was set at 50°C, which corresponds to a DME vapor pressure of 150 psig. Refueling was accomplished by mixing the diesel fuel and DME onboard the bus, with diesel fuel delivered from the existing diesel tank and DME delivered by 1000 Ib cylinders at a small refueling station. The shuttle bus operates on the Faculty/Staff loop at the University Park campus of the Pennsylvania State University.

STATIC CALIBRATION METHODOLOGY FOR WEIGH-IN-MOTION SYSTEMS

A weigh-in-motion (WIM) static calibration methodology is described and demonstrated. The calibration procedure quantifies WIM response variation across the width of WIM sensors. A simple methodology is described to track wheel path location across a WIM system. With knowledge of WIM sensitivity variation across sensor width, along with wheel trajectory location, this methodology offers the possibility of improvement in WIM system performance. The specific WIM system studied was shown to be minimally affected by temperature and results suggest improvements in installation technique. This static calibration methodology complements, but does not replace, typical WIM dynamic calibration requirements.

Weigh-In-Motion studies using strip-type sensors : the preliminary results

The various conditions of dynamic vehicle tire forces on pavement loading have been investigated by using strip type commercially available piezo-electric Weigh-In-Motion (WIM) sensors. Usually, the WIM load is found by empirically relating the peak voltage of the signal to the static wheel weight, and the area under the signal and the vehicle speed are not considered. A formula considering the area under the WIM signal and the moving load is presented. Whether or not static calibration factor of strip type sensors is sufficient to calculate the vehicle dynamic load is determined and a quasi-static vehicle pass over calibration methodology for future experiments is suggested. This paper also reviews the detailed description of the research carried out on existing WIM sensors and related systems.

DIMETHYL ETHER (DME)-FUELED SHUTTLE BUS DEMONSTRATION PROJECT

The objectives of this research and demonstration program are to convert a campus shuttle bus to operation on dimethyl ether, a potential ultra-clean alternative diesel fuel. To accomplish this objective, this project includes laboratory evaluation of a fuel conversion strategy, as well as, field demonstration of the DME-fueled shuttle bus. Since DME is a fuel with no lubricity (i.e., it does not possess the lubricating quality of diesel fuel), conventional fuel delivery and fuel injection systems are not compatible with dimethylether. Therefore, to operate a diesel engine on DME one must develop a fuel-tolerant injection system, or find a way to provide the necessary lubricity to the DME. In this project, they have chosen the latter strategy in order to achieve the objective with minimal need to modify the engine. The strategy is to blend DME with diesel fuel, to obtain the necessary lubricity to protect the fuel injection system and to achieve low emissions. The bulk of the efforts over the past year were focused on the conversion of the campus shuttle bus. This process, started in August 2001, took until April 2002 to complete. The process culminated in an event to celebrate the launching of the shuttle bus on DME-diesel operation on April 19, 2002. The design of the system on the shuttle bus was patterned after the system developed in the engine laboratory, but also was subjected to a rigorous failure modes effects analysis with help from Dr. James Hansel of Air Products. The result of this FMEA was the addition of layers of redundancy and over-pressure protection to the system on the shuttle bus. The system became operation in February 2002. Preliminary emissions tests and basic operation of the shuttle bus took place at the Pennsylvania Transportation institutes test track facility near the University Park airport. After modification and optimization of the system on the bus, operation on the campus shuttle route began in early June 2002. However, the work and challenges have continued as it has been difficult to maintain operability of the shuttle bus due to fuel and component difficulties. As of late June 2002, it appears that the pump head itself developed operational problems (loss of smooth function) leading to excessive stress on the magnetic coupling and excessive current draw to operate. A new pump head is being installed on the system to alleviate this problem and get the shuttle bus back in operation. In summary, the conversion is completed but there have been operational challenges in the field. They continue to work to make the shuttle bus as reliable to operate on DME-diesel blends as possible.