Internal-combustion engines – Precombustion and main combustion chambers in series – Vaporizing in precombustion chamber
Reexamination Certificate
1998-07-03
2002-01-22
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Precombustion and main combustion chambers in series
Vaporizing in precombustion chamber
C123S258000, C123S270000, C123S292000
Reexamination Certificate
active
06340013
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to piston-type internal combustion engines having a single piston and an exhaust heat recuperator which preheats the compressed air charge and passes it into a pre-chamber for combustion. The invention relates further to an engine having a recuperator and a protective valve to protect the recuperator from the combustion process.
2. Description of the Related Art
Internal combustion engines today, with the exception of Diesels, operate on what is commonly known as an Otto cycle originally patented in France in 1862 by Alphonse Beau de Rochas. In 1876, the Rochas compression cycle was incorporated into a practical engine by Nicholas A. Otto. Otto engines were immediately more efficient than Lenoir non-compressing gas engines which had been in production since 1862. Then in 1892, Rudolf Diesel invented the compression ignition engine with higher efficiency than an Otto engine. At the time, their efficiencies were about 3 to 4% for the Lenoir, 12% for the Otto, and 24% for the Diesel, and compared with their expansion ratios of approximately 1.5: 1, 2.5: 1, and 16: 1.
The low efficiencies are related to the large amount of energy remaining in the engine exhaust at the moment of release by the exhaust valve. Exhaust temperatures of 1,450° Fahrenheit or more for example were reported for the Lenoir and Otto, and around 900° F. for the Diesel. Actual gas temperatures inside the cylinders when expansion was complete were surely much higher. This is because a great deal of heat transfers to the exhaust valve and then to the exhaust port walls. For example, gas reaches about 90% equilibrium with wall temperature after flowing only ten diameters along the length of a straight pipe. In early engines, exhaust valves and ports were labyrinthine in design and thus absorbed much of the heat from the exhaust before it exitted the engine.
The better efficiency of the Diesel came about due to its very high expansion ratio, a result of the high compression ratio needed to create high temperature sufficient to auto-ignite the injected fuel. The high compression ratio and attendant gas and bearing pressures required greatly increased strength and with it, increased weight and cost. In fact, the Diesel is two to three times the weight and cost of a comparable Otto engine.
In present day Otto engines such as those used in automobiles, compression/expansion ratios are typically around 8:1 and expansion of the combustion gases is far from complete. Thus, at full load, exhaust is released at 90 to 120 pounds per square inch and 2,500 to 3,200° F. and carries away to the coolant and the atmosphere nearly half of the input fuel energy.
A partial solution to energy wastage with the exhaust has been the turbo-expansive conversion of exhaust energy to rotative energy, the rotative energy then being used to drive a turbo-compressor for boosting input air pressure to an engine. Turbines however cannot tolerate direct exhaust heat from an Otto engine nor are they suited to the pulsating exhaust flow from a single cylinder. Exhaust from several cylinders is merged to smooth the flow and passed through exposed pipes to dump part of the heat to the atmosphere so as to cool the gases by 1,000 to 1,500° F. Exhaust turbines have thus been only minimally effective in raising the efficiency of Otto engines.
Recuperative gas turbines were developed for stationary use beginning around 1950 wherein residual exhaust heat is captured and returned to the compressed air before it enters the burners. Gas turbines operate on the Brayton gas cycle and differ from the Otto cycle in that combustion takes place at constant pressure and that expansion continues typically back to atmospheric pressure. Brayton and Otto cycles are similar however in that the exhaust exitting from a gas turbine is usually at a higher temperature than the compressed air entering the combustion chamber. The opportunity thus exists for a reduction in the fuel input required, since the heat being exhausted can be used (at the cost of a heat exchanger and connecting ducting) to provide part of the heat input, with consequent increase in efficiency. A brief review of the regenerative gas-turbine cycle may be found in
Engineering Thermodynamics
by M. C. Potter and C. W. Somerton, McGraw-Hill, 1993. A more complete analysis of recuperative gas turbines may be found in
Marine Gas Turbines
by John B. Woodward, John Wiley & Sons, 1975.
Gas turbines with heat exchangers are under development today for military use as evidenced by a request for proposal published in the Department of Defense Fiscal Year 1998 Small Business Innovation Research (SBIR) Program #A98-013 Titled:
Advanced Ultra Compact Heat Exchangers
. In this request, it is noted that present day, state-of-the-art recuperated gas turbine engines use metallic heat exchangers which are exceedingly heavy and larger in volume than all the engine turbomachinery components combined, thereby precluding their use in air vehicles.
In the prior art, recuperative engines have generally had adequate recovery of exhaust heat but their transfer of heat to the working charge has been inefficient. This is because the high temperature, high grade thermal energy available in and recovered from the exhaust has been allowed to degrade prior to its transfer to the working charge. Early inventors of heat engines sought effective use of recuperators, but often compromised thermal efficiency by reducing temperatures either to protect working materials and surfaces or to avoid problems with detonation or pre-ignition in the combustible mixture.
The first known recuperative internal combustion engine of the prior art is described in U.S. Pat. No. 155,087 granted Sep. 15, 1874 to Joseph Hirsch. It has two cylinders in a vee plus an air pump adjoined at their working ends by a duct containing a regenerator and is described as a hot-air engine.
In U.S. Pat. No. 328,970 granted Oct. 27, 1885, inventor James F. Place describes a recuperative engine that uses two stage, counter-flow transfer of exhaust heat to the compressed charge. Place used two cylinders approximately 70° apart in phase to provide separate compression and expansion in his engine.
Looking now at the art related to single piston recuperative engines, U.S. Pat. No. 1,190,830 granted to J. F. Wentworth describes a single cylinder engine having transfer of exhaust heat to the incoming air charge. Since the transfer is prior to compression, the engine cycle is not advantageously recuperative. Wentworth recognized at an early date, the utility of a thermally insulating liner in the combustion chamber and on the piston cap to reduce heat losses from combustion. The refactory metal liner was separated by a space from the cylinder head and the space filled with a refractory insulation such as asbestos.
U.S. Pat. No. 1,945,818 granted to H. L. McPherson and J. W. Weatherford describes an engine with no recuperator but having a separated combustion chamber connected by a duct to a single cylinder with a reciprocating piston therein, the piston being shaped to provide minimum clearance with the cylinder head. Fuel input and a spark plug provide for combustion within the chamber while a poppet valve controls gas flow through the duct between the chamber and the cylinder. The poppet valve is perforated by holes
23
, believed to be for cooling.
U.S. Pat. No. 2,671,311 granted to H. Rohrback is similar to the engines of some of the earlier patents in the use of a liquid coolant, in this instance, by injection of coolant into the cylinder after the work stroke to cool the cylinder and piston. A condenser for the volatized liquid coolant acts as a heat exchanger to heat air being drawn therethrough for injection into the cylinder by a supercharger. The Carnot efficiency of this engine would not be significantly improved since the cycle is not recuperative.
U.S. Pat. No. 3,591,958 granted to William H. Nebgen and assigned to Treadwell Corporation, teaches the use of an external turbo-compressor to
Argenbright Tony M.
Schaeffer Patent Agent Daniel M.
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