Yes you’ve read that right. BMW believes that the solution to increase power output from a turbocharged petrol engine is to inject water, and we’re not talking about the radiator or intercooler here, but literally injecting water directly into the combustion chamber.
Earlier this year, BMW debuted a novel water injection technology in the M4 MotoGP Safety Car. Since then, the technology have progressed further, evolving into direct water injection and have been adapted for use in a prototype 1-series (pre-LCI model) fitted with a modified 1.5-litre three cylinder engine.
BMW says its direct water injection technology overcomes the main hurdle with turbocharged engines – that power output is affected by high temperature of the compressed air that is being fed into the engine, thus limiting the compression ratio, which subsequently limits the engine’s power output.
The temperature in the combustion chamber is also directly proportionate with harmful NOx emissions. So cooling the compressed air that’s coming into the engine’s intake manifold not only increases performance, but also reduces NOx emissions.
In the M4 MotoGP Safety Car, located in the boot is a five-litre water tank. With the aid of a high pressure pump and sophisticated control electronics, water is then injected into the engine’s intakes at 10 bars of pressure.
The water is injected as a fine spray into the intake manifold plenum chamber where it evaporates, extracting energy from its surroundings and reducing combustion temperatures in the engine by around 25 degrees Celsius. In the case of the 1-series prototype, the system has been improved further to inject water not just into the intake manifold, but also directly into the combustion chamber.
In most turbocharged engines, the engine’s computer usually injects a tiny amount of fuel to cool combustion chamber before delivering more fuel for combustion. With direct water injection, this process is no longer necessary and BMW reckons that the system can reduce real-world fuel consumption by 8 percent.
With better control of the combustion chamber’s temperature, the prototype 1-series’ three cylinder turbocharged engine’s compression ratio can now be increased from 9.5:1 to 11.0:1, which BMW says will improve power and torque by up to 10 percent.
With lower combustion temperatures comes reduced risk of ‘knocking,’ so the engine can now reliably run on lower octane RON95 fuel despite the high 11.0:1 compression ratio.
How often must the water tank in the boot be refilled? In the case of the M4 MotoGP Safety Car’s twin turbo straight-six 431 PS engine driven under racing conditions, the tank needs to refilled at every fuel stop.
However BMW says the system that will be fitted into production BMWs in the future will require almost zero maintenance as the tank refills itself by recovering waste condensed water vapour from the vehicle’s air-conditioning system.