Multi Fuel Closed-loop Thermo Cycle Piston Engine



A small to medium sized automobile that gets about 25 MPG and the engine is developing approximately 20 BHP wile consuming 2.5 GPH at freeway speed. The amount of thermal energy being used is 2.5 X 2546 BTU/HP = 51,000 BTU wile consuming 2.5 GPH at 120,000 BTU per gallon for a total of 300,000 BTU. Admittedly these are approximations. Some estimates are that the Otto cycle efficiency is as high as 38% when operating at max torque. But most agree that 20 to 25% is normal operation.


 To restate, 50,000 BTU is being used while 300,000 is being created. The 250,000 BTU of heat energy remaining is mostly being dumped into the environment. This efficiency data is published in a study by the Environmental Protection Agency.


The object of this engine design is to reduce the amount of thermal energy losses such that the highest possible amount of fuel energy is used to perform the engine work.

This design has many characteristics of a gas turbine in that a wide variety of fuels can be used wile maintaining the same thermal efficiency.



 An externally fired continuous combustion constant pressure engine that uses water injection “post combustion” to transform the maximum amount of thermal energy into gas pressure that drives the piston type engine.


This engine is comprised of a separate compression stage, a combustion stage and an expansion or drive stage. The combustion is located outside the engine and uses “Continuous Combustionthen water injection “Post Combustion” to transform the maximum possible thermal energy at into gas at a constant volume and low temperatures into the expansion stage.


The amount of water injection is controlled via the “Electronic Control Unit” such that as work is extracted, the energy remaining in the exhaust is minimized. The temperatures of the exhaust gasses can be held to near ambient thus minimizing the energy wasted via the exhaust. The input to the expansion stage is therefore allowed to float in accordance with the work of the engine.

Pressure sensors are incorporated such that the fuel input is limited by the ECU such that the pressure remains within a specified limit at any throttle input and the fuel is increased automatically as the RPM of the engine is increased.


This technique allows for a greater amount of thermal energy recovery than can be obtained from an exhaust heat recovery system.


Since the temperatures of the working gas into the expansion stage is low, metallurgical limitations due to high temperatures are eliminated. Thermal losses due to absorption of heat into the mechanical parts of the engine is minimized substantially reducing or eliminating the need for an engine cooling system.

 This design also makes possible the incorporation of additional techniques that permits pre-combustion water injection in the fuel burner chamber to control combustion temperature thus reducing NOX emissions without sacrificing thermal efficiency.


Thermal energy recovery to be recycled back into the engine is not practical with the Otto cycle or Diesel engines. These engines may be characterized as “Batch Fired Engines”. A turbine on the other hand is a continuous combustion engine.

Dr Dah Yu Cheng is credited with the development of an energy recovery from the exhaust to be recycled into a turbine engine dramatically increasing the efficiency of the engine which became known as the “Cheng Cycle”.

Cheng Cycle turbines are widely used as high efficiency engines in the electric power generating industry, A system that incorporates a similar principle into small piston engine has never been successfully developed.

In normal operation the efficiency of the automobile is about 20 to 25%. The efficiency of a diesel is slightly higher usually around 30% however the diesel efficiency remains relatively constant at varying throttle settings due to constant compression. This engine design will produce its maximum torque at minimum RPM and the greatest thermal efficiency exists in the range it is most often used.

Engine Design and Hardware description

The technique of using “POST COMBUSTION” water injection to transform thermal energy into working gasses as well as reducing internal temperatures has been tested, This technique although not workable in a turbine it can be adapted in a piston engine. It performs the same function as an exhaust heat recovery system more efficiently and with less hardware.

Key to the success is the Fuel Burner design and the issues of control incorporated into the Electronic Control Unit along with a post combustion water injection technique.

Air is pumped into an external combustion chamber where fuel is burned. Water is then injected into the heated gasses at the outlet end or “Post Combustion” end of the burner chamber creating steam. This steam pressure together with the gasses produced by the combustion drive the remaining cylinders.

The exhaust valves of the compression cylinders that pump air to the burner chamber are pressure operated where the intake valves are camshaft operated. This is essential to the design in that it establishes a ratio between the compressed volume and the expanded volume that is applied to the drive cylinders. Constant pressure is applied to the expansion or drive cylinders for the full power stroke. Variable spring pressure is used to increase RPM operation.

Basically, the pressure developed in the burner is only reached by the compressor cylinders near the top of the stroke where maximum mechanical advantage of the crankshaft rotation reached. Conversely the pressure applied to the pistons of the expansion cylinders during the full stroke or at least to the point of their maximum velocity and mechanical advantage of the crankshaft rotation is reached. The difference of this pressure profile will widen as pressure is increased due to the power developed by the fuel combustion applied to the resistance of the load.


The Combustion chamber is comprised of an outer pressure container with an inner combustion liner where the fuel is burned. Since all the air pumped by the compressor cylinders is not needed to support combustion some of the air flows between the combustion liner and the outer pressure container. This provides thermal isolation between the Pressure container and the combustion liner. Some experimentation was conducted to create additional isolation by injecting a finely atomized water spray into this area which is carried to high temperature end of the combustion liner by the air flow where it is then mixed with the high temperature gasses at outlet of the combustion liner by a series of baffles placed at the hot end of the combustion chamber.

The mixing baffles were placed at the “HOT” end of the burner outlet just after the “Post Combustion” water injection is to provide homogeneous mixing and cooling of the gasses. Cooling of the baffles is provided by the water. The baffles are angled in the flow to create an eddy to maximize thermal mixing.

The temperature monitoring thermocouple that controls “Post Combustion” water injection is located at the expansion stage output.

Water injection “Pre-Combustion” may also be used to reduce combustion temperatures at high pressures to reduce NOX emissions and is also controlled by the ECU as a function of pressure.

By controlling the “Post Combustion” water injection via an electronic control system {ECU) in accordance with a temperature monitor placed at the at the exhaust of the expansion cylinders such that the temperature of the gasses discharged from the exhaust is minimized (Usually less than 100 degrees C), the engine operates at maximum possible thermal efficiency. The ECU controls the temperature monitored at the output of the expansion cylinders independent of throttle by adjusting the water injection at the output of the burner.

It is also essential to the design that the ECU maintain “Full authority” over the fuel input. The fuel input is limited as a function of pressure to prevent over-fueling at lower RPMs.

Since this is also a function of the thermal energy of the fuel varying fuel energies do not affect the engine performance. Thus, any mixture of ethanol or fossil fuels, either liquid or gas will produce no noticeable effect on engine performance.

10 years of prototype testing was necessary to develop the previously described concept.



* This engine is relatively simple in hardware design and substantially less complex than existing Otto cycle or Diesel engines and should be substantially less expensive to produce.

* The engine requires little or no cooling system reducing the hardware needed.

* The engine is a true “Flex Fuel” engine that will operate on the same thermal efficiency using almost any type of combustible liquid or gas fuel or fuel mixtures.

* The engine is reasonably expected to have a fuel efficiency of about 250% greater than that of an Otto Cycle.

* Water injection is a proven method of reducing exhaust emissions. Reduction of fuel used logically reduces resulting emissions. Continuous combustion allows for increased combustion control reducing emissions. Combustion temperatures can easily be reduced thus reducing or eliminating NOX emissions without sacrificing thermal efficiency at high compression ratios.

* The engines maximum torque is produced at the lowest RPM thereby enabling the engine to be operated at its highest efficiency in most normal operation.

* This engine is more efficient than a Hybrid and is substantially less expensive to produce and maintain.