Split-cycle aircraft engine

1. A split-cycle air hybrid aircraft engine comprising:

a crankshaft rotatable about a crankshaft axis;

a power piston slidably received within a power cylinder and operatively connected to the crankshaft such that the power piston reciprocates through an expansion stroke and an exhaust stroke during a single rotation of the crankshaft;

a compression piston slidably received within a compression cylinder and operatively connected to the crankshaft such that the compression piston reciprocates through an intake stroke and a compression stroke during a single rotation of the crankshaft;

a gas crossover passage operatively interconnecting the compression cylinder and the power cylinder, the gas crossover passage including an inlet valve and an outlet valve defining a pressure chamber therebetween;

an air reservoir operatively connected to the pressure chamber by a reservoir passage at a location between the inlet valve and the outlet valve of the pressure chamber, the air reservoir being selectively operable to receive compressed air from the compression cylinder and to deliver compressed air to the power cylinder for use in transmitting power to the crankshaft during engine operation;

valves selectively controlling gas flow into and out of the compression cylinder, the power cylinder, and the air reservoir;

wherein the engine is mounted to an aircraft and the air reservoir is disposed within the aircraft;

wherein the engine is operable in a high pressure (HP) mode, in the HP mode:

the compression cylinder is selectively controllable to operate as a power cylinder having an expansion stroke and an exhaust stroke; and

both the power cylinder and the compression cylinder receive compressed air from the air reservoir which is expanded on the compression and power cylinder's respective expansion strokes and discharged on their respective exhaust strokes.

2. The split-cycle air hybrid aircraft engine of claim 1 , wherein the aircraft has wings, the air reservoir being disposed in the wings.

3. The split-cycle air hybrid aircraft engine of claim 2 , wherein the aircraft has a wing spar in each wing, the air reservoir being disposed in at least one of the wing spars.

4. The split-cycle air hybrid aircraft engine of claim 1 , wherein the aircraft has a cockpit, a tail, and an aft fuselage proximate the tail, the air reservoir being disposed in the aft fuselage.

5. The split-cycle air hybrid aircraft engine of claim 4 , wherein the air reservoir is disposed proximate the tail.

6. The split-cycle air hybrid aircraft engine of claim 1 , wherein the compression cylinder is selectively controllable to place the compression piston in a compression mode or an idle mode.

7. The split-cycle air hybrid aircraft engine of claim 1 , wherein the power cylinder is selectively controllable to place the power piston in a power mode or an idle mode.

8. The split-cycle air hybrid aircraft engine of claim 7 , wherein the engine is operable in at least an internal combustion engine (ICE) mode, an air compressor (AC) mode and a pre-compressed air power (PAP) mode, and wherein:

in the ICE mode, the compression piston and power piston are in their respective compression and power modes, in that the compression piston draws in and compresses inlet air for use in the power cylinder, and compressed air is admitted to the power cylinder with fuel, at the beginning of an expansion stroke, which is ignited, burned and expanded on the same expansion stroke of the power piston, transmitting power to the crankshaft, and the combustion products are discharged on the exhaust stroke;

in the AC mode, the compression piston is in the compression mode and draws in and compresses air which is stored in the air reservoir for later use in the power cylinder; and

in the PAP mode, the power cylinder is in the power mode and receives compressed air from the air reservoir which is expanded on the expansion stroke of the power piston, transmitting power to the crankshaft, and the expanded air is discharged on the exhaust stroke.

9. The split-cycle air hybrid aircraft engine of claim 8 wherein, in the PAP mode, fuel is mixed with the compressed air at the beginning of an expansion stroke and the mixture is ignited, burned and expanded on the same expansion stroke of the power piston, transmitting power to the crankshaft, and the combustion products are discharged on the exhaust stroke.

10. The split-cycle air hybrid aircraft engine of claim 8 wherein, in the PAP mode, the compressed air admitted to the power cylinder is expanded without adding fuel or initiating combustion.

11. The split-cycle air-hybrid aircraft engine of claim 1 wherein:

in the power cylinder, fuel is mixed with the compressed air at the beginning of an expansion stroke and the mixture is ignited, burned and expanded on the same expansion stroke of the power cylinder; and

in the compression cylinder, compressed air admitted to the compression cylinder is expanded on the expansion stroke of the compression cylinder without adding fuel or initiating combustion.

12. The split-cycle air hybrid aircraft engine of claim 1 , wherein fuel is ignited within a range of 5 to 40 degrees crank angle (CA) after the power piston has reached its top dead center (TDC) position.

13. The split-cycle air hybrid aircraft engine of claim 12 , wherein fuel is ignited within a range of 10 to 30 degrees crank angle (CA) after the power piston has reached its top dead center (TDC) position.