New developments in water injection and turbocharging

Water and petrol do mix, apparently

Water and petrol seems an unlikely combination to put in your car - they certainly don’t mix very well - so why is one of Germany’s top car makers planning to inject water into the engines of its new petrol models?

The news coming out of Bavaria is that BMW will be using water injection technology on all its turbocharged petrol engine cars in an effort to squeeze more power and better fuel consumption out of them.

The science behind water injection and turbocharging

It’s all about overcoming the limits to turbocharging petrol engines. There’s a limit to how much turbocharging boost you can apply to a petrol engine before the combustion chambers get so hot that the mixture of fuel and air explodes before it should. It’s called knocking, and you really don’t want it in an engine.

Injecting water into the combustion chamber lowers the temperature and allows BMW to increase compression ratios and turbo boost pressures, holding out the promise of more power while using less fuel on full throttle.

A brief history of water injection

The technology has been around in race and rally cars for several years and BMW is now keen to get it into all its petrol models, which are all turbocharged. However, the technology may still be a little way off as Bosch, which supplies BMW, is still a little wary about guaranteeing the longevity of its fuel pumps and injectors delivering the water and petrol.

The idea has been around for a long, long time. Piston engine military aircraft were using it before WW2 to wring more power out of the engine at take-off, enabling them to use shorter runways and climb faster. Some fighters used water injection to provide a bit more “oomph” to the motor in short bursts in the midst of dogfights.

Find out more

Find out more

It’s not even new in cars. The 1962 Oldsmobile F85 had a turbocharger and used a mixture of 50/50 methanol and distilled water to overcome the problem of knocking. The innovative SAAB 99 Turbo S also came with water injection in 1979-80.

Water injection generally gave way to intercoolers as the preferred way to reduce combustion chamber temperatures, but water injection does promise one other benefit on top of increased power. It potentially reduces nitrogen oxide and carbon monoxide emissions in exhaust, making for cleaner air.

Does this mean new BMW owners will reaching for the garden hose?

Well no, because those clever Bavarians have figured out that most of the time the condensation from the car’s air-conditioning system, which normally just drips onto the road, will be enough to supply the system, with perhaps the occasional top-up of distilled water. That’s certainly the case in hot climates like ours.

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Categories: Technology, Fuel
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