Internal combustion engines go green

Nowadays the internal combustion engine seems to be a little outdated compared to the far greener batteries that power electric cars, but when it comes to green credentials the ordinary internal combustion engine is not dead yet; engineers and scientists are developing the next generation internal combustion engine which will emit less than half of the greenhouse gasses emitted by current engines.

The problem with current engines is that they are very inefficient: only 25% of the fuel burned is converted into motion; the other 75% is lost as heat. Consequently the obvious way forward is to recover that heat and convert it into motion.

40% of the engine output is wasted in the exhaust, and some of it can be recovered by installing a turbine into the exhaust pipe. The turbine drives an electrical generator and the electrical energy can be stored and used to power the electrical systems on the car. The amount of energy that can be recovered in this manner is relatively high. In a normal family saloon car around 6 kilowatts can be recovered, which is sufficient to cut fuel consumption and emissions by around 15%.

The other major area of energy recovery is the kinetic energy lost in braking, and today’s hybrid cars, which combine an electric motor and internal combustion engine, are already fitted with kinetic energy recovery braking systems which convert recovered kinetic energy into electrical energy. The recovered energy is stored in batteries and used to power the electric motor. However there is an even better way of doing this.

The new system is called a super fly and instead of converting the energy to electricity and to store it in order to drive an electric motor, the super fly eliminates the conversion process and stores the energy as pure kinetic energy.

The Formula One racing team Williams carried out a considerable amount of work on KERS (kinetic energy recovery system) based on this principal, though it wasn’t actually used in racing cars as the electrical conversion process was easier to implement.

Several prototype cars with super fly KERS have now been built and trialled. These have a flywheel that is directly linked to the gearbox. When the driver depresses the brake pedal the flywheel is engaged and the kinetic energy that is used to accelerate it also slows the car down. The flywheel has negligible friction and so continues to rotate until the driver reapplies power. When the driver presses the accelerator, the kinetic energy stored in the flywheel is applied through the gearbox to the cars drive train. The system is completely automatic and needs no additional input from the driver. The system recovers 70% of braking energy, over twice as much as with conventional hybrid cars.

Another way of improving energy efficiency is by replacing the highly inefficient piston cylinder arrangement with one in which the combustion chamber itself expands. The concept is known as the Internally Radiating Impulse Structure or IRIS engine and it could improve fuel efficiencies by as much as 50%. However it has not yet got any further than the drawing board and computer simulations.

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