Concept: A Rotary Engine Based on a New Thermodynamic Cycle

18 May 2006

A sketch of the LiquidPiston Engine.

A father and son team—Dr. Nikolay Shkolnik, an entrepreneur and inventor, and his son Alexander, a PhD student at MIT—have developed an engine architecture they claim will achieve 50% fuel efficiency (compared to the ~30% of existing engines) and drastically reduce pollutant emissions.

The architecture, based on a patent-pending “High-Efficiency Hybrid Cycle” (HEHC) thermodynamic cycle, borrows elements from Otto, Diesel, Atkinson and Rankin cycles. LiquidPiston, Shkolnik’s company, is implementing the HEHC cycle in a rotary piston engine: the LiquidPiston Engine.

(In April, LiquidPiston was named one of the four finalists in the ECOnomics Environmental Business Plan Challenge presented by GE & Dow Jones. The ECOnomics winner will be announced this month and receive a $50,000 prize.)

The HEHC Cycle. The basic cycle uses a discrete compression chamber, isolated combustion chamber, and expander chamber.

Air (with no fuel) is compressed to a high ratio (> 18) in a compressor cylinder of the engine. The resulting compressed charge is directed into an isolated combustion chamber, where fuel is injected and auto ignites.

Combustion occurs under truly isochoric conditions (volume stays constant) and is allowed to complete until all fuel is fully combusted. The combustion products then expand into the expander cylinder, which has large volume than the intake volume.

Optionally, a small amount of water may be used to facilitate cooling, lubricating and sealing of combustion chamber and pistons.

A small amount of water (an optional component) may be used in the system. Water may facilitate the cooling, lubricating, and sealing of combustion chamber and pistons.

The Liquid Piston engine. A) full housing. B) Transparent housing showing principle components. Click to enlarge.

The Liquid Piston Engine (LPE). The HEHC cycle can be implemented in a variety of ways; LiquidPiston is developing an implementation that uses a separate rotary compressor, two isolated combustion chambers, and a separate rotary expander.

Each Combustion Chamber (CC) rotates at constant speed, and simultaneously acts like two valves, one of which regulates flow between the compression chamber and the combustion cavity (through the Compressed Air Port), and the other valve which regulates flow between the combustion cavity and the expansion chamber.

The operation of the four cylinders is such that all four strokes occur simultaneously within the engine.

The compressor begins on the right side, and moves counterclockwise, with center of rotation around the lower bearing. This motion induces the compression stroke in the left compression cavity, and intake stroke in the right compression cavity.

This is followed by combustion in the left combustion chamber, which occurs in complete isolation from both the compression and expansion cavities. After combustion completes, combustion products meet the Expander Piston (EP).

The EP is in the left most position, and moves counterclockwise, with center of rotation around the upper bearing. Combustion products from the left combustion chamber drive the EP, which induces the power stroke in the left expansion cavity, and exhaust in the right expansion cavity.

After 60 degrees of rotation, the pistons stop their motion and switch their centers of rotation. The engine, which is symmetric in its operation, now undergoes another cycle of 4 strokes just as described above, except that all roles of the cylinders and combustion chambers reversed.

The result is an engine with the following projected characteristics (with respect to Otto or Diesel engines of similar power specifications):

• Significantly improved engine efficiency, reaching 50%

• Reduced size and weight by 50%

• Reduced parts count by 85%

• Reduced NO_x emissions by 70%

• Reduced CO₂ emissions by 50%

• Low friction design leading to long life

• Decreased maintenance requirements: no oil or spark plug changes required,

• Less noise, due to low pressure exhaust and absence of poppet valves

Although it may appear similar to a Wankel, the rotary LPE is based on a different thermodynamic cycle, and avoids the sealing and combustion issues affecting the Wankel design.

LiquidPiston is currently seeking seed funding from investors and government grant funds to build an alpha-prototype to establish the feasibility of the proposed High Efficiency Hybrid Cycle Engine.

(A hat-tip to Shaun Mann!)

Resources:

• High Efficiency Hybrid Cycle Engine (ICEF2005-1221)