The present invention also relates to a multistage internal-combustion engine with the addition of compressed air in one or more stages after the first one.

Background Art As is known, internal-combustion engines of the conventional type (Otto or Diesel cycle) are not very efficient and in particular they do not utilize adequately the heat energy generated by the combustion of the fuel.

A considerable fraction of the heat energy is lost with the exhaust gases, which are expelled at very high temperatures and pressures.

Combustion does not occur in an optimum manner and the exhaust gases are highly polluting.

Various kinds of engine having a plurality of stages in series with a plurality of expansion units are also known.

These engines are particularly complicated, although they can reach higher efficiencies than conventional engines.

Disclosure of the Invention The aim of the present invention is to provide a high-efficiency internal- combustion engine.

Within this aim, an object of the present invention is to provide an internal-combustion engine with high heat recovery.

Another object is to provide an internal-combustion engine that uses external energy sources of the alternative and/or renewable type.

Another object is to provide an internal-combustion engine whose emissions produce low pollution.

Another object is to provide an internal-combustion engine that has a simple structure.

This aim and these and other objects that will become better apparent hereinafter are achieved by an internal-combustion engine with separate and optimized compression, combustion and expansion strokes, comprising a multistage compressor, which compresses air and sends it, cooled and compressed, to a combustion-expansion unit into which fuel is introduced by means of a high-pressure pump, the exhaust of said combustion-expansion unit being connected to a second expansion unit, which is also supplied with compressed air that is cold or heated by means of exchangers that cool the stages of said multistage compressor.

Brief description of the Drawings Further characteristics and advantages of the invention will become better apparent from the following detailed description of the engine of the present invention, given by way of non-limitative example in the accompanying drawings, wherein: Figure 1 is a diagram of the engine; Figure 2 is a view of the cycle of the engine.

Ways of carrying out the Invention With reference to Figure 1, an engine according to the invention, shown schematically, is composed of a multistage compressor 1, which in the specific case is shown with three compression stages, designated by the reference numerals la, 1b and lc respectively.

The compressor is driven by a motor ld, which can be of any kind and in particular, in fixed systems, can utilize an alternative energy source of the renewable type, such as for example wind power, while in other cases the compressor 1 is driven by the engine itself once it has reached the steady state.

The stages of the compressor 1 are cooled by means of first heat exchangers 2 and 3, which dissipate heat, as will become better apparent

hereinafter.

Said heat can be recovered fully or partly by heating air and recovering the heat energy generated by the compressor 1.

The air compressed by the compressor 1 passes through a third exchanger 4 and is sent to a combustion-expansion unit 5, which is constituted by a piston 5a that moves with a reciprocating motion within a combustion chamber 5b.

The fuel drawn from a tank 6 is pumped by a high-pressure pump 7 and can also be heated by an exchanger 8 connected to the exchanger 4.

The fuel is introduced through a duct 9 into the combustion chamber 5b.

The combustion emissions, through the duct 10, are conveyed from the combustion chamber 5b to a second expansion unit 11, which comprises an expansion chamber lla within which a second piston 11b moves with a reciprocating motion.

Air, optionally heated by the first two exchangers 2 and 3 or by heat recovery processes and compressed by a second compressor 13, is also sent into the expansion unit 11 by way of a duct 12.

As can be seen from the illustrated diagram, heat recovery is very high and the exhaust gases that exit at 14 from the second expansion unit 11 have a very low pressure and temperature.

The engine according to the invention operates as described in the cycle of Figure 2.

As can be seen, the theoretical cycle consists of the following steps: A-B: lys'stage for compression of a certain amount of atmospheric air; B-C: cooling of a fraction of the air compressed in the first stage; C-D: 2 stage for compression of the cooled air fraction; D-E: cooling of a fraction of the air compressed in the second stage.

E-F: 3rd stage for compression of the air (Note: additional stages of compression and cooling may follow); F-G: constant-volume combustion, avoiding cracking;

G-H: constant-pressure combustion; H-1 : expansion in the combustion-expansion unit 5 (1 S working step); I-L + B-L: mixing between a fraction of the air compressed by the first compression stage and burnt gases discharged from the cylinder 5, to be expanded in the second expansion unit 8 (with heat recovery from the cooling of the multiple compressor) L-M: expansion in the cylinder 8 (2nd working step).

The motor ld of the compressor 1 can be replaced advantageously with a power take-off driven by the engine itself once it has been started; in this manner, just one auxiliary starter motor is needed.

Compression is performed with a multistage compressor as regards the air required for combustion.

This system allows to achieve high pressures at the end of the compression cycle, with low temperatures, such as to avoid the endothermic phenomenon of cracking, which reduces the efficiency of the engine.

This system also allows high turbulence, which cannot be achieved with any other system, with an enormous advantage for flame propagation.

The engine is characterized in that feeding occurs at the top dead center of the piston, with advance or delay.

Power is adjusted according to the volume made available by the piston, and pressure and temperature remain always optimized.

The volume of the filling chamber can also be generated by a piston located on the head and arranged opposite the piston of the engine. Upon combustion, such second piston can generate a reversible work, again for reducing the phenomenon of cracking.

The injection of the air and fuel can also be modulated in a subsequent step.

In addition to the air required for good combustion during the expansion stroke, it is possible to introduce air at a suitable temperature and pressure, so that the exhaust gases exit at a pressure and temperature that are close to

ambient values.

Such air is introduced through the same inlet valves and mixes with the products of combustion, exhaust gases that in normal engines reach approximately 3-4 bar and 700-750 °C, so that the exhaust gases exit at a temperature and pressure that are close to ambient values.

This additional expansion can occur with the piston of the engine itself, sized appropriately, or with an additional piston or gas turbine. The advantage of this second option would be that it would be possible to interpose a catalytic converter, which operates at high temperature and pressure, with a considerable catalytic effect.

The advantage of the exhaust temperature close to the ambient temperature is that it allows to reduce particulates with simple filters or with a water sprinkler.

In the first case it is possible to use textile filters and in the case of the sprinkler, in view of the temperature, the evaporation effect does not occur or is limited.

Significant advantages of the engine: -- recovery (like dynamos) of the braking effect by means of the compressor, which accumulates compressed air in the tanks; -- the ability to recover all renewable energies, from wind power to photoelectric cells to large or small water falls to tides, accumulation energy; in the case of wind power, it can be transported to the point of use by means of air pipelines ; -- it is also possible to recover, particularly in the case of gas-fueled engines, the energy of gas pipelines without resorting to interstage expansion heating processes, because the engine itself provides the heat energy; -- a theoretical characteristic for which this engine is intended is that no heat escapes at all except by means of mechanical energy.

The preceding description describes a preferred implementation of the claimed invention in a preferred embodiment. However, it should be

appreciated that other implementations and applications may be devised without departing from the scope of the invention as claimed.

Materials, dimensions and components may be chosen appropriately without altering the inventive concept.

The disclosures in Italian Patent Application No. PD2002A000168 from which this application claims priority are incorporated herein by reference.