| 14 January 1999
For Immediate Release
Advanced Natural Gas Vehicles Begin Fleet Testing
Starting this month, The Johns Hopkins University Applied Physics Laboratory (APL), Laurel, Md., will begin testing a fleet of three, unique natural gas-powered automobiles.
What sets these natural gas vehicles (NGV) apart is that they are the first "fully capable," compressed natural gas-dedicated, mid-size sedans. They push back the limited utility and driving range of current OEM-offered NGVs that are found in the "niche" markets of taxicabs, police cars and gas utility service cars. In most respects, APL's advanced NGVs are virtually indistinguishable from their gasoline-fueled counterparts except for the method of refueling and their ultra-low exhaust emissions.
These technology demonstration NGVs are based on the DaimlerChrysler JA-series (Plymouth Breeze, Dodge Stratus, and Chrysler Cirrus) sedan. The "fully capable" label refers to the fact that these cars have a city/highway driving range in excess of 300 miles, provide ample trunk space for luggage, and offers the performance and reliability found in today's gasoline-powered cars.
These prototypes were developed under APL's Advanced Natural Gas Vehicle (ANGV) program, cost-shared by the U.S. Department of Energy Office of Advanced Automotive Technologies and the Gas Research Institute. The work was conducted with a team assembled by APL that included DaimlerChrysler, Lincoln Composites, Siemens Automotive, Goodyear Tire and Rubber Corporation, Chesapeake Automotive Enterprises, Craig Naff, Inc., and Hegedus Aluminum Industries, Inc. The engineering development for these vehicles has taken place over four years using a systems approach to solve tough design and manufacturing problems in three areas: the engine, gas storage, and vehicle packaging.
To derive the maximum benefit from natural gas as fuel, developers made a number of critical modifications to the stock gasoline engine. The engine, a derivative of DaimlerChrysler's 2.4-liter DOHC, was outfitted with forged aluminum, high-compression (12.5: 1) pistons, hardened nickel-tungsten exhaust valve seats, a state-of-the-art, multi-point gaseous fuel injection system, and a methane-specific catalytic converter. Powertrain development included both engine and chassis dynamometer testing. The Powertrain Control Module software was developed by Chrysler Engineering. The powerplant delivers excellent performance, high fuel mileage, and ultra-low exhaust emissions.
Growth of the NGV automotive market growth has been hampered by the fact that compressed natural gas storage cylinders are bulky, costly, and not readily amenable to vehicle packaging. Thus, light-duty NGVs generally have a shorter driving range than gasoline fueled cars and have significant loss in trunk space. The ANGV team has solved these problems by developing the Integrated Storage System, or ISS.
The ISS uses lightweight, all-composite, small-diameter cylinders (termed "pressure-cells") encapsulated within a high-strength fiberglass shell with impact-absorbing foam. This arrangement unitizes the pressure-cells into a single container and protects the pressure-cells from external impact abuse as well as environmental exposure. All ISS operating valves, interconnection gas lines, and safety devices (collectively defined as the gas control system) are completely integrated and protected from damage with a removable fiberglass cover.
An essential feature of the ISS is that it is similar in shape to a conventional gasoline tank, greatly simplifying vehicle packaging. Another important fact is that the ISS is secured to the chassis with steel straps, allowing the car's "crumple-zone" to work as intended in a rear-end collision.
The ISS lowers costs by reducing the amount of costly carbon fiber in the pressure-cell overwrap without sacrificing safety, by simplifying the gas control system for multiple CNG cylinders, and by providing the container as a complete unit ready for installation. The ISS has been extensively tested and complies with Federal Motor Vehicle Safety Standard FMVSS#304 and other NGV-industry safety standards.
The ANGV prototypes use two ISS containers: one 3-cell unit is mounted in the undercarriage, and a 2-cell unit is located in the trunk behind the rear seat. The two containers provide a total capacity of 12.0 gge (gasoline gallons equivalent) at a service pressure of 3,600 psi.
To create space in the vehicle chassis for the ISS units, developers modified the rear undercarriage and trunk bulkhead regions. In the undercarriage, the stock OEM lateral-link, rear-suspension system was replaced with a custom-developed, semi-trailing arm suspension, and a flat floorpan was installed in place of the spare tire wheel well. To compensate for the absence of a spare tire and jack, the cars are equipped with Goodyear Tire & Rubber Company Extended Mobility Tires(tm) (i.e., "run-flat" tires).
The semi-trailing arm rear suspension is based on a design found in a number of contemporary gasoline-fueled automobiles. The semi-trailing arms are cast from a high-yield strength, high-fatigue life aluminum alloy. The arms are outfitted with toe-adjustable bushings and interface directly with the OEM strut, hub, and brake assemblies. Extensive CAD modeling and static load tests were conducted to ensure that the modified rear suspension design was safe. In road tests, the vehicle's handling matches or is slightly superior to the OEM stock arrangement.
The ANGV chassis design and use of run-flat tires is not intended to show a design unique to NGVs. Rather, these vehicle features are increasingly found in contemporary cars as weight-saving and safety features. The ANGV design demonstrates a common platform for mass-producing either a dedicated CNG or gasoline-powered automobile without compromises. The next step is to evaluate the cars in normal, everyday driving. The cars have entered the APL auto pool and data is being gathered on "real-world" driving range, reliability, and aged exhaust emissions. This will provide an opportunity to gather valuable information for automakers, government officials, and transportation planners.
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