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Chrysler A-831 Automobile Turboshaft
Many people know that the Chrysler Corporation developed a gas turbine powered production automobile in the 1960's. What many do not know is that apart from Chrysler, numerous automakers including Ford, GM, Austin, Rover, Fiat, and Volkswagen also worked on developing turbine powered road cars and race cars. Aircraft turbine engine makers even joined the fray, including Williams International, Turbomeca, and Pratt&Whitney, to develop automotive based turbines.
While others were in on the fun as well, The 1963 Chrysler Ghia Turbine Car was the closest we ever saw in a turbine powered production automobile. On May 6, 1963, Chrysler announced that they would be selecting 200 customers to sample one of these turbine powered cars for three months, as part of a marketing research program. Chrysler carried out this program successfully, and presumably collected a great deal of data on consumer feeling toward the vehicle, which was generally positive. Ultimately, a true production line of turbine cars was never produced, but the Chrysler Ghia Turbine was as close as it got.
Powering the Ghia was a purpose built free shaft gas turbine engine, designed and produced by Chrysler Corporation, which was referred to under the designation A-831. Due to the fact that this engine would be powering a road vehicle, there are vast differences in the design requirements between it and a typical aircraft gas turbine engine. The A-831 was a dual shaft, free shaft gas turbine shaft engine with a power output of 130 brake horsepower @ 3,600 rpm. Much more impressive was its peak torque of 425 lb/ft at stall rpm. While this output doesn't seem all that impressive, especially for an engine weighing 410 lbs., in 1963 this was considered an impressive power to weight ratio. Power to weight ratio wasn't Chrysler's major concern, anyway. Fuel economy, drivability, and ease of operation were most important in the development of a production turbine engine. Consider that the primary structure of the engine was made of cast iron to save production costs, and that, in general, low cost materials and manufacturing processes were used, and one can understand better the general design philosophy of the engine.
Air was drawn into an upward facing, screened scroll inlet which also served as a housing for the accessory drive shaft coming off the front of the compressor. From the intake housing, air is drawn into the single stage centrifugal compressor, which rotated at a maximum of 44,600 rpm. Air from the compressor discharge was fed to two rotary regenerators, which were a gas turbine heat exchanger technology that was almost exclusive to automotive applications due to its compact nature. Two honeycombed rotating discs, driven at very low rpm (approximately 22 rpm) off of the accessory drive, would operate in both the compressor discharge path and the power turbine outlet path. As a section of the disc would pass through the exhaust portion, the hot exhaust gas would pass through the honeycomb, heating the disc. As that part of the disc rotated around to the intake portion, compressor discharge air was made to flow around the outside of the disc, and through the honeycombed sections. The disc's heat would be transferred to the compressor discharge air, heating it from a compressor discharge temperature of about 450 degrees F to a temperature of approximately 1200F. The increased temperature of the air coming into the combustor would mean less fuel was required to reach a set turbine inlet temperature, which meant a fuel savings.
From the regenerator, the air would travel into a scroll type combustor. Fuel was delivered to the combustor via an air atomizing nozzle, which used compressed air, supplied by a small engine driven reciprocating pump. The A-831 engine, as most of the automotive turbine engines of the time, had a continuous ignition system which was basically a standard automotive ignition without breaker points but without a distributor cap, as there was only one spark plug. While the engine was running, the plug would continually spark, to provide an auto-relight feature in the event of a flameout during deceleration.
From the burner, the hot combustion gases travelled to the single stage axial gas producer turbine, which drove the compressor and the accessories. From the gas producer turbine, the gases then traveled past a variable geometry power turbine nozzle before driving the single stage axial free power turbine. Variable turbine nozzles were the other major element common on many automotive turbine engines. Variable turbine nozzles are a necessity for an application such as this, as they allow much finer control over power turbine speed and torque over the full rpm range, allow for engine braking, and also improve part power and idle fuel consumption, a definite weak point for any gas turbine engine. The nozzles were controlled by a single cam controlled hydraulic actuator, which received power from the lubrication pump. Actuator position was scheduled by accelerator pedal position and engine speed. At starting and idle speeds, the nozzle would be fully opened, allowing for the largest possible nozzle area. As the accelerator pedal was depressed, the nozzle area would become increasingly small, increasing turbine inlet temperature and power until the speed increased to the point where the nozzles would have to begin opening again to allow the greater flows. When the accelerator pedal was released, the nozzles would move in a reversing direction, causing a degree of aerodynamic coupling between the power turbine and the gas producer spool while providing a braking effect on the power turbine wheel. Once vehicle speed dropped below 15 mph, the nozzle would return to its open position. Variable nozzles were key to the gas turbine's success in this application.
The power turbine was directly coupled to a Torqueflight-8 3 speed automatic transmission, without a torque converter, although subsequent development versions of the powerplant utilized a torque converter for various reasons, one reason being that in subsequent versions, most of the engine accessories were relocated to the power turbine shaft to unload the gas producer; meaning that the power turbine could not be stalled or else the accessories would stop turning.
The exhaust gas passed through the two rotary regenerators before being expelled through two exhaust ducts that would make their way to the rear of the car. One concern about using gas turbine engines in an automotive application is that the hot exhaust of the turbine would be a hazard to pedestrians and other automobiles. In truth, with the regenerator, the exhaust gas temperature coming out of the tailpipe was actually cooler than many piston engine exhausts of the time. One downside was the much greater volume of airflow coming out of the tailpipe.
Accessories in the A-381 were driven from an accessory gearbox mounted on the very front of the engine, driven by a shaft coming forward off of the compressor which drove helical pinion and geartrain. Accessories included the fuel pump and hydromecanical fuel control unit, lubrciation pump, starter generator, and regenerator drive.
After Chrysler's test program was completed, there were two other developments beyond the A-381 engine, each with their own set of improvements over the previous. And while the turbine car did prove that a turbine engine could do as good a job as the gasoline piston engine in an automobile, it still wasn't enough to justify the greater cost, and most importantly, the greater fuel consumption at idle and low power settings, which an automobile engine spends most of its time doing. This hurdle was never overcome, and when the fuel crisis hit in the 1970's it was the final nail in the coffin for the automotive turbine concept. The turbine engine was never again revisited for use in a large scale production automobile application, until recently, where the concept of a turbine/electric hybrid car has been considered by engineers and designers around the world.
Chrysler A-831 Automotive free shaft gas turbine engine
For more information about the Chrysler Turbine car, check out these sites:
Also, for more information about automobile gas turbine engines, read Jan P. Norbye's great book, "The Gas Turbine Engine" Click here for link
Special thanks to www.allpar.com for turbine car images.
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