Connecticut Company Unveils Prototype of New Small Engine Technology - The X Mini

The LiquidPiston X Mini is reportedly 30% smaller and lighter, with fewer moving parts and less vibration.

The LiquidPiston X Mini Engine
The LiquidPiston X Mini Engine
Liquid Piston Logo 546e4bede6f69

A Bloomfield, CT-based company is seeing if it can shake up the small engines business over the next couple of years.

LiquidPiston has been around since 2003, but just this November introduced a prototype of its 70cc four-stroke gasoline engine at a conference in Italy. The company says it is now talking with outdoor power equipment manufacturers about potential applications.

LiquidPiston is currently in talks with several potential partners/OEMs and hopes to have the engine on the market in the next two years,” says Dr. Alexander Shklonik, president and co-founder of LiquidPiston. “In the first quarter of 2015, LiquidPiston will host a call for ideas for potential uses for the engine. Given that this is a brand new engine—and is smaller, lighter and more efficient—it could enable brand new applications that don’t even exist today. The company will award a cash prize for the most innovative idea and will likely then develop the engine for that application as well.”

Small in size, big on performance. Because of the engine’s patented HEHC thermodynamic cycle and engine architecture, the X Mini is reportedly 30% smaller and lighter than comparable four-stroke piston engines, and could enable many small engine applications to be smaller, lighter and quieter. Additionally, it offers a high power-density ratio of up to 2 horsepower per pound. Furthermore, the X mini has just two primary moving parts, a rotor and an eccentric shaft. Except for ancillary parts such as injectors, fuel pumps and oil pumps, there are no other moving parts—greatly reducing complexity.

The Alpha Protype was just introduced in November. The product will now move through to a Beta Protype, and finally a Mature Commercial Design that’s ready for market in the next two or three years. Key performance specs (comparing today’s Alpha Protype and the projected Mature Commercial Design) include:

  • Gasoline fuel; PFI (port fuel injection) or carbureted  —  Multi fuel-capable, including diesel, gasoline, natural gas, JP-8; direct injection
  • 9.2 compression ratio  —  10.5 compression ratio
  • 1 injector, 1 rotor  —  1 injector, 3 rotors
  • 3.5 hp  —  > 5 hp
  • 13,000 rpm  —  15,000 rpm
  • 4 pounds (dry weight)  —  3 pounds (dry weight)
  • 221 cubic inches (6.6” x 6.2” x 5.4”)  —  180 cubic inches (6” x 6” x 5”)
  • 0.9 hp/pound  —  1.7 hp/pound
  • Time between overhaul: 3 hours  —  1,000 hours

Let’s get technical

LiquidPiston’s X Engine architecture is a non-Wankel rotary embodiment of the company’s innovative High Efficiency Hybrid Cycle (HEHC). The X Engine has few parts and three combustion events per rotor revolution, resulting in tremendous power density, the company says. Additionally, LiquidPiston’s X Engine architecture geometry allows for standard materials and 2-D manufacturing to be used, greatly decreasing the design, build and testing cycle.

LiquidPiston’s HEHC is a patented thermodynamic cycle that combines the advantages of Diesel, Otto and Atkinson thermodynamic cycles. The cycle elements include:

  1. Compression: For maximum efficiency, air is compressed to a high compression ratio, fuel is injected and compression ignited (CI-HEHC). The X Mini utilizes a spark-ignition (SI-HEHC) version of the cycle with a lower compression ratio standard for gasoline engines.
  2. A dwell near top-dead-center forces combustion to occur at nearly constant-volume conditions.
  3. Combustion products are over-expanded using a larger expansion volume than compression volume, as in the Atkinson Cycle.
  4. Cycle-skipping power modulation allows high efficiencies at low power settings while simultaneously cooling the engine’s walls internally and providing partial heat recovery.
  5. Water may be injected to internally cool the engine. Some of this cooling energy is recuperated, as the water turns to steam, increasing the chamber pressure.
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