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Concept: VGT Developing “Plug-in” Gasoline/Compressed Air Hybrid Based on the RoundEngine

Basic design of a two-piston RoundEngine. Click to enlarge.

Canada’s VGT Technologies, the developer of the RoundEngine, has started development of a “plug-in” compressed air hybrid vehicle using the RoundEngine technology. In this application, “plug-in” refers to connecting to an external air compressor to top off the storage tanks. The RoundEngine is a novel variable geometry toroidal (VGT) engine.

The gasoline/air hybrid vehicle is similar to a gasoline/electric hybrid vehicle but uses compressed air instead of electricity for an auxiliary drive. In the first phase of development VGT will focus on the air drive using the RoundEngine technology by modifying an AWD vehicle to incorporate the air drive on the rear axle. The front axle will be powered by the gasoline engine. The purpose is to prove the air drive in an automotive application and to demonstrate fuel and emissions savings. VGT is manufacturing a toroidal engine for this application.

In the first phase of the project, the air drive will be used mostly for acceleration and low speed, while the gasoline engine powers the car at higher speeds and recharges the air tanks. The system will support regenerative braking, and offer the optional plug-in capability to recharge airtanks in off-peak hours. The compressed air can be used to supercharge the combustion engine for short periods without any mechanical supercharger resulting in short power boosts.

In the second phase, VGT plans to apply waste heat from the exhaust and the engine cooling system to the compressed air and converting the expansion/pressure increase into power. Other options are to use fluids with phase changes to produce closed cycle high pressure steam for propulsion.

The third phase of development will focus on a dual-engined vehicle. There will be two RoundEngines, a combustion version and an air motor version. One engine will run on air only while the other RoundEngine will operate with a combustible fuel.

The RoundEngine. VGT was formed to commercialize the variable geometry toroidal engine developed by Rudy Pekau beginning in 1995. In 2002, VGT developed a 625 cc, single-cylinder prototype engine which used compressed air as a power source. In 2004/05, VGT converted the air-powered motor to a combustion prototype.

The external combustion chamber. Click to enlarge.

The RoundEngine is a toroidal rotary engine with two or more pistons fixed around a central disc that connects to the drive shaft, replacing the connecting rods and crankshaft. Combustion occurs in a external combustion chamber, with the gases venting into the toroidal chamber to move the pistons. Inlet, exhaust and combustion chamber valves are set in the base of the toroidal track.

A rotating timing disc, the shaft of which is tangential to the toroid, provides a means for the pistons to compress fresh air and is a backstop which prevents combusted air from moving back through the housing. As a piston passes an inlet port, the air is compressed between the piston and the timing disc until a valve opens upstream of the disc to allow the air charge to flow into the external combustion chamber. The combustion chamber is closed and a direct-injected fuel charge is ignited, then exhausted through a valve on the side of the timing disc.

The disc has a cutout to allow passage of the piston. By the time the combustion chamber exhaust valve opens, the piston has passed through the cutout, and the timing disc once again seals the track.

With two firings per revolution of the output shaft, a two-piston RoundEngine is equivalent to a conventional four cylinder, four-stroke design. VGT suggests that on large engines a second combustion chamber could be used, 180° away from the first.

The RoundEngine can vary two volumes. By using multiple inlet ports, the choice of which can be switching during operations, the engine can vary the volume—and hence displacement—of the compression stroke. Because the combustion chamber is external to the toroid, the actual working internal volume within the chamber can be increased, or decreased. This feature has more of an impact on fuel choice and compression ratios, but nonetheless can also be used to some degree to impact displacement.

VGT does note yet have empirical evidence for power from the engine, but has calculated a range of outputs. For example, a 2-piston, 2.4-liter displacement RoundEngine operating with a pressure ratio of 1.5 to 1 should deliver 88 bhp at 1,500 rpm and 134 bhp at 3,000 rpm, with 310 lb-ft and 236 lb-ft of torque, respectively.

VGT suggests that initially, the RoundEngine can achieve savings of 15-35% in fuel consumption over reciprocating combustion engines and smaller gas turbines.




@ Anne wrote :
"I think he had the smarter option of solar thermal power in the desert in mind"

No argument from me but he said 'solar power'. I'm not psychic yet so I don't know that he actually meant solar thermal, he simply put "solar power" To me that usually infers PV. Although as you point out grid fed thermal is the more economical & practical way to go.

I would add that recently an inventor friend informed me that PV is catching up as they attempt to capture a much wider portion of the solar spectrum. Optimised into three separated bandwidths, but other than that, the subject is somewhat outside my sphere of interest.

Lad introduced both supply side and demand side economics into his post.
Let's now look at the demand side which is a consideration of battery economics-

A123's assertion of their product possessing thousands of cycles capability would change the calculation regarding economics but that has yet to been proven in full scale mass production. Come to that we have no useful figures for NIMH either since the Prius uses its battery in a way that is significantly more forgiving on the pack performance (or lack of it) than a BEV will be.

Strictly BEVs are O/T here since the round engine targets PHEVs with the air storage.(see website)

However.. @Hank
Many ICE costs are time variant rather than distance variant. Therefore they don't do short distance comparisons well. In that scenario, a Li-ion BEV will successfully compete if calendar life is good but it may still have to survive many recharge cycles during that time as per A123's assurance.

Of course, if the cost per pack could be reduced by about one eighth even if it came with a poor calendar life (perhaps 3 years) I maintain they could still be successful. This is exactly the role that lead acid plays. Lead acid has proven successful over the decades with Stand n' Drive milk delivery floats.
I expect you will find these vehicles with transverse motor mounting to the reduction gearing for high mechanical efficiency. Although it has to be said that the antiquated control systems of the 19th century together with series field DC motors yielded a less than desired dynamic performance.

Lead acid in more contemporary electric delivery (hiway capable) vans has not continued this success. Although solid state controllers should have given them good dynamic performance there were no useful increases in range because the higher speeds were hampered by poor aerodynamic efficiency. That and the fact that they were mechanically inefficient because they generally borrow an existing platform and much of the transmission designed for the original gasoline motor.

In the right application which is for any consumer, living in a temperate climate, who will except range and performance limitations of around 90 miles at 75mph and zero to sixty in eight seconds, a custom designed vehicle like the EV1 will be entirely successful with lead acid.

On the otherhand if Li-ion cycles don't measure up with high mileage usage and replacement becomes necessary, then a Prius hybrid or non hybrid would have been the better choice. It will remain speculation until droves of BEVs are on the road.

Simply put, BEV models with exotic chemicals must run 15 years else lead acid at one eighth the cost is still viable. I'll install $2000 of lead acid to get a 12 y.o. car going again, but $16,000 Li-ion no way.

michael Bryant

I just realized something. Compress air is perfect for trains. A compress air power train can have very large air tank to gave it grate range.

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