LiquidPiston to develop fuel-efficient rotary combustion engine technologies for US military

be especially useful with turbocharged engines that today run at lower compression ratios, to avoid over-stressing the engine when the turbocharger is forcing more air into the combustion chambers. The patent was sought by Porsche’s huge consulting arm along with Porsche client Hilite International, suggesting the engine technology might be offered to other automakers if and when it’s made commercially viable.

Technology has raised compression ratios to 11:1 or 12:1 and as high as 13:1 in Mazda SkyActiv cars. Premium-grade gasoline allows for higher compression ratios than regular. Knock sensors can adjust ignition timing to avoid detonation. Still, design engineers have to back off on the base compression ratio when there’s a turbocharger involved, which affects efficiency at low rpm, which reduces mpg in the vehicle and its desirability to the buyer. It also makes the car feel like a pig when your first tromp on the throttle (turbo lag). Enter the variable-compression-ratio engine and Porsche’s new technology.

Porsche and Hilite conceived a way to adjust the apparent length of the connecting rods, the metal arms that connect to the crankshaft and drive the pistons up and down. A solenoid allows small oil-pressure-driven rods and an eccentric adjuster to raise or lower the bearing supporting the piston. The patent diagram appears to show a high and low position currently, not a variable height. Today’s gasoline-engine cars compress the outside air to about a tenth its original volume, a 10:1 ratio, inside each cylinder. Compress it more and you get detonation – also called knock or ping – before the spark plug ignites the air-fuel mixture at or near top dead center, when the piston is at the top of its travel.

Since Porsche is a consulting group as well as an automaker, and in some years in the past made more money off consulting, this is likely to be a technology with the possibility of being adopted throughout the industry on small engines — just as Mitsubishi’s balancer shafts are now common on almost every four-cylinder engine. These designs also show that the gasoline internal combustion engine will continue to be the dominant powerplant in passenger cars.

From patent to engine in production could be several years. Even a relatively simple design needs to be tested for durability and quirks that might show up outside the lab. Still, engines of the last 25 years have become increasingly more complex without any falloff in basic reliability. Hilite International makes components used in variable valve timing controls (VVT) that run reliably despite their complexity.

The car starts off with the piston in the high position. When the turbo begins injecting pressurized air, the piston drops to the low position. That reduces the compression ratio momentarily, allowing for more turbocharger boost and more power. The Porsche-Hilite design appears to be comparatively simple, at least compared to other variable-compression-ratio efforts that date back a century.

LiquidPiston has signed an agreement with the US Defense Advanced Research Projects Agency (DARPA) to develop fuel-efficient, lightweight, rotary combustion engine technologies for the US military. The company has already developed prototypes that have validated the principles and confirmed compression ignition of diesel and JP-8 fuels.

According to the LiquidPiston, increase in military engine fuel efficiency will save lives of soldiers who transport and protect fuel on the front lines and are prone to attack, and save money in fuel and transportation logistics costs, while reducing the military's carbon footprint.

In addition, the move could help extend mission times by allowing engine-powered equipment, like unmanned air vehicles to operate longer on the same amount of fuel, while enable lighter, more compact equipment designs and further improving operational range and payload capabilities.

"A typical 3kW heavy-fuel generator weighs over 300lb, requiring six people to move it around.

"LiquidPiston's engine technology may enable a JP-8 generator of similar output weighing less than 30lb that could fit in a backpack."

The agreement focuses on demonstrating a pathway to a heavy-fuelled engine that can deliver more than 50% average brake efficiency, 57% peak brake efficiency and high-power density using a test-bed environment, which will reduce fuel consumption by approximately one half, compared to legacy piston engines.

LiquidPiston is funding 40% of the project, which will demonstrate key enabling components of the engine technology, as well as initial experiments with JP-8, a kerosene-based jet fuel used widely by the US military. Under the $1m agreement, the company will advance the development of its highly efficient, power-dense rotary internal combustion engine for portable and small-engine applications.

LiquidPiston will demonstrate a pathway towards a rotary Jet Propellant 8 (JP-8) fuelled engine that can lower fuel consumption by 50% and increase power density.

LiquidPiston Founder and chief technical officer and DARPA effort co-principal investigator Dr. Nikolay Shkolnik said: "Today's diesel / JP-8 engines and generators are extremely heavy.

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