Stirling engines are unique heat engines because their theoretical efficiency is nearly equal to their theoretical maximum efficiency, known as the Carnot Cycle efficiency. Stirling engines are powered by the expansion of a gas when heated, followed by the compression of the gas when cooled. The Stirling engine contains a fixed amount of gas that is transferred back and forth between a “cold” end (often room temperature) and a “hot” end (often heated by a kerosene or alcohol burner). The “displacer piston” moves the gas between the two ends and the “power piston” changes the internal volume as the gas expands and contracts.
Air in the engine is cyclically heated (by an alcohol burner) and expands to push the power piston (shown in blue) to the right. As the power piston moves to the right, the yellow linkage forces the loose-fitting, red “piston” (on the left half of the machine) to displace air to the cooler side of the engine. The air on the cool side loses heat to the outside world and contracts, pulling the blue piston to the left. The air is again displaced, sending it back to the hotter region of the engine, and the cycle repeats.
The Stirling engine cycle can also be used “in reverse”, to convert rotating motion into a temperature differential (and thus provide refrigeration).
Air-powered hybrid car unveiled.
Peugeot Citroen have shown off a hybrid car which can run on petrol or compressed air, or a combination of both.
The ‘Hybrid Air’ system uses a petrol engine for travelling at ‘cruising’ speeds, where the makers say petrol is still the most efficient power source. At slower speeds or when the vehicle needs extra power to climb a hill, the car uses a combination of compressed air and petrol. At slower speeds below 43mph the car runs solely on compressed air until the supply runs out.
The air tanks are refilled during all modes of driving, by re-using energy normally lost during slowing down and braking, instead using that energy to run an air compressor. The makers claim an average fuel saving of 45 percent, and when driving solely around cities at slower speeds that figure could rise to 80 percent.
The car is expected to be available by 2016.
The Lancia Triflux engine is Beautifully Engineered
The Lancia ECV car originally produced over 600 horsepower (448 kW) from a 1759 cc twin-turbocharged engine. This engine, christened Triflux, was built in an unusual fashion; the valves were crossed (for each side of the cylinder there was an intake and an exhaust valve), so that the two turbochargers could be fed with two separate manifolds. A single manifold carried the intake air (hence the name, from the three separate air ducts).
The twin KKK turbochargers can be linked in a modular turbocharging unit, with a single turbo being used at low revs to build up power and then, when the revolutions are right, the second turbo comes into play to take the power even higher. With such a unit, high torque is produced at low revs with no loss of maximum power and greatly reduced turbo lag.
The system produces improved heat distribution in the cylinder head to even out the expansions that take place on a turbo unit, also helping to improve engine cooling. It is now possible to link a single central wastegate valve to the two exhaust manifolds and, if the latest variable geometry turbochargers are utilised, the wastegate can be eliminated altogether.
The air that leaves the turbochargers is injected into the radiators or intercoolers before being passed on to the induction manifold and thence back into the cycle, while the compactness of the engine allowed the engineers much more freedom to plan the exhaust system to eliminate resonance problems encountered in more crowded systems.
- Centrally mounted, longitudinal with 4 cyl inline.
- 1795CC. Bore x stroke, 88.5mm x 71.5mm
- Triflux’ double reverse flow cylinder head with 4 valves/cylinder and twin overhead camshafts.
- Compression ratio, 7.5:1
- 600bhp @ 8000rpm
- Twin KKK (K26 type) turbochargers with individual intercoolers.
- Weber/Magnetti Marelli injection/ignition with electronically controlled turbocharging level.
- Dry sump lubrication with pressure and extraction pumps and air/oil radiators.
Mitsubishi Lancer 2000 Turbo (Group B car)
- Engine: 1997cc Inline 4 cylinder (4G63 “Sirius Dash”)
- Bore: 85 mm
- Stroke: 88.0 mm
- Head: SOHC 8 Valve
- Fuel: ECI
- Induction: Forced (MHI Turbo)
- Power: 280PS @ 7000 rpm
- Torque: 33.7kg-m @ 5000 rpm