Isolated Combustion and Diluted Expansion (ICADE) Piston Engine

The present invention relates to an improvement in thermal efficiency, and exhaust pollution of an internal combustion piston engine. More specifically the invention separates the combustion process from the cylinder by means of an isolation valve. The high temperature exhaust products are admitted into the cylinder where they mix with compressed air to form a reduced temperature mixture prior to piston expansion. This invention not only permits operation at a very lean overall mixture, but also allows high compression ratios without engine "knock".

Many patents have been filed on techniques to enhance the lean burning ability of internal combustion piston engines. They are listed under stratified charge engines. Although an ideal spark ignition engine has a thermal efficiency which is only a function of compression ratio and not of combustion temperature, in practice it is found that combustion efficiency improves when burning lean mixtures, if combustion is fast and completed prior to piston expansion. Unfortunately lean mixture burn slower than stoichiometric mixtures, which results in heat addition during piston expansion with loss in combustion compression and thus thermal efficiency. The slow burning problem lowers the efficiency of a conventional natural gas engine at high RPM. An example of a solution to the lean burning problem is the recent modification of the Mitsubishi engine, each cylinder has two intake ports and one exhaust port. One of the two intake ports conducts only air while the other conducts a richer air/fuel mixture. The spark plug is closer to the air/fuel intake than to the air only intake. Ignition starts at the side were the mixture is richer and spreads rapidly and evenly throughout the chamber.

The "Isolated Combustion and Dilution Expansion (ICADE) Engine", is a piston/cylinder arrangement used primarily for the compression of air and the expansion of diluted hot combustion products. Fuel injection and combustion takes place inside a separate combustion chamber. The combustion compression provides the pressure needed to inject the combustion products tangentially into the donut shaped cavity formed by the piston/cylinder clearance. There they establish a vortex which enhances rapid mixing, rapid cooling to quench NO.sub.x forming reactions and to temporarily store the kinetic energy of the combustion products to limit the combustion pressure peak acting on the piston surface.

Only during the compression stroke, is the combustion chamber isolated from the piston/cylinder arrangement, by a valve with "controlled leakage". During the compression stroke, this "leaky valve" prevents the combustion chamber pressure from rising as high as the pressure inside the cylinder. Installing and controlling air flow in such a "leaky valve" is easier than using a valve which seals hot combustion products as specified in some of the referenced patents. The controlled pressure difference provided by the "leaky valve" serves several purposes.

a) It prevents fuel injected inside the combustion chamber from leaking into the piston/cylinder arrangement

b) It allows combustion air to enter in the form of a high turbulent jet to produce good mixing with the fuel.

c) It allows use of a rapid burning near-stoichiometric combustible mixture, while the overall air/fuel mixture ratio can be below the lean flammability limit.

d) It permits the use of a low octane fuel at a moderate compression ratio inside the combustion chamber, while using high compression ratio inside the cylinder, to maintain high thermal efficiency.

e) It can replace the engine throttle valve as it controls the amount of combustion air admitted and thus the engine power level, without need to reduce the cylinder compression ratio and thus thermal efficiency.

This engine is especially suited for slow burning alternate fuel, such as natural gas, as it permits fuel injection throughout the compression stroke and good mixing with the turbulent combustion air jet. The tangential injection of the combustion products and associated vortex provides rapid mixing and quenching so as to halt NO.sub.x forming reactions, prior to piston expansion. The resulting lean mixture permits after burning of any remaining unburned hydrocarbons.

The tangential cylinder injection permits the application of detonation combustion for faster burning and higher combustion compression. The detonation shock wave enters parallel to the piston surface thereby preventing normal shock wave reflection with its associated "knock". The detonation generated kinetic energy is only available for a few micro-seconds and should be lost unless it is stored as vortex kinetic energy, such as is done in the ICADE engine. Some of this kinetic energy is recovered in the form of pressure during expansion.

The ICADE engine is the only one of its kind capable of efficiently harnessing shaft power from a detonation combustion. The herein described improvement in internal combustion engines is applicable to both spark ignition as well as compression ignition engines of either two or four cycle types. It promotes rapid combustion and the "leaky valve" is able to provide power control without need to throttle the cylinder intake air. The "leaky valve" permits operation at a cylinder compression ratio well above that allowable inside the combustion chamber to avoid pre-ignition. This means performance at high thermal efficiency at all power levels. Separating the combustion process from the cylinder allows operating with an overall fuel/air mixture ratio well below the lean flammability limit.

FIG. 1 is a cross-section of the ICADE Piston Engine. It shows the donut shaped cavity formed by the piston/cylinder head in which the vortex is formed.

FIG. 2 is a top view of the cylinder. It shows the combustion chamber entering tangentially into the donut shaped cavity

FIG. 3 is a cross-section of another ICADE Piston Engine configuration. It uses a conical piston for radial diffusion, mixing and dilution instead of a donut shaped cavity as in FIG. 1

In FIG. 1 is shown a section of the piston/cylinder arrangement used by the Isolated Combustion And Dilute Expansion (ICADE) Piston Engine. This ICADE engine improvement is applicable to all spark ignition and compression ignition engines of either two or four cycle designs. The connecting rod (1) and crankshaft are conventional but with a long stroke to piston diameter ratio in order to get a high compression ration. Two major modifications are in the piston (2) and cylinder head (3), both are cupped so that together they form a donut shaped cavity (4), with the piston at top dead center. The cupped section of the piston must extend beyond the cylinder (5) to make from for the cut-out required by the tangential entry for the products of combustion which come from a separate combustion chamber (6). This chamber is placed in line with the tangential entry as clearly shown in the top view of FIG. 2. At the far end of the combustion chamber is a fuel valve (7), which during the compression stroke, provides direct fuel injection, with or without atomization air, into the combustion chamber. Ignition timing is not controlled by the fuel injection process as it is in the Diesel cycle. When the piston nears top dead center, ignition is provided by either a spark plug (8), or by compression ignition following rapid opening of valve (9), which isolates the combustion chamber from the cylinder during the compression stroke. Valve (9) has a controlled leakage rate which, during the compression stroke, keeps the pressure inside the cylinder higher than in the combustion chamber. This pressure differential prevents fuel from escaping into the cylinder and permits compression ignition upon rapid opening of valve (9). Valve (9) is shown as a gate valve but could also be a pull-to-open valve, as long as the valve is fully out of the way into recess cavity (10) during the remainder of the cycle. The valve support arm (11) is spring loaded in such a way that spring (12) tries to keep the valve open and also function as a torsion spring to keep the valve seated. The valve seating force is augmented by the pressure differential across the valve. Following ignition the combustion chamber pressure must increase beyond that in the cylinder. At ignition, the valve (9) must be open, so as not to obstruct the flow of the products of combustion into the donut shaped cavity where they form a vortex, mix with the compressed air and are quenched prior to piston expansion. The dilution to a very lean overall air/fuel mixture reduces the temperature inside the cylinder, the formation of NO.sub.x and cylinder wear. To prevent damage to valve (9) by excessive pressure force, in the case of pre-ignition with the valve still closed, the valve is capable of pivoting out of the way, against the action of the torsion spring (12). The inlet and outlet valves (13) and (14) are conventional. Inlet valve (13) is placed in line with the combustion chamber outlet, with its inlet port opposing the combustion chamber in order to minimize scavenging. The exhaust valve (14) port is directed so as to take advantage of the vortex momentum inside the cylinder for minimum pressure loss exhaust.

In FIG. 3 is shown an alternate configuration for the ICADE Piston Engine. Here the piston (16) is conical and at top dead center, makes a close fit in the cylinder heat (17). The conical point of the piston contains a spring loaded pull to open type valve (18) which functions as the combustion chamber (6) isolation valve just like valve (9) shown in FIG. 1. The separate combustion chamber is mounted on top of the cylinder head and in line with the piston centerline. Some of the high dynamic pressure of the combustion products is recovered during a source flow like diffusion after they are deflected radially out by the conical tip of the piston.