Future tech: BMW direct water injection
With direct water injection for turbocharged gasoline engines, BMW has again succeeded in pushing the envelope of conventional engine technology through an process of refinement and improvement. The precisely controlled injection of water into the engine cylinders produces a cooling effect that boosts power and torque, particularly when operating at or near full throttle, while at the same time reducing fuel consumption and emissions.
Water injection made its debut in a modern-day BMW Group engine under the bonnet of the BMW M4 MotoGP Safety Car. Designed by BMW M GmbH for M4 high-performance sports car, it is powered by a modified version of the high- revving M TwinPower Turbo six-cylinder in-line engine that already develops 431 hp and 405 lb-ft. Water injection provides the M4 MotoGP Safety Car with extra power, torque and efficiency for its duties on the race track.
At the BMW Group Innovation Days 2015, this innovative technology in a prototype of a core BMW model, in its latest-generation three-cylinder engine. In this version of the system, most of the water is injected directly into the combustion chamber, rather than just into the intake manifold. In the prototype, which is based on a 5-door BMW 1 Series, direct water injection offers an optimised balance between driving pleasure and fuel consumption in keeping with the principle of Efficient Dynamics.
Direct water injection allows the potential of turbocharging to be harnessed even more effectively. 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° Celsius. Particularly at full throttle, this cooling effect provides a big improvement in efficiency, while helping to improve the combustion process in other ways.
For instance, the cooling effect provided by water injection reduces temperatures sufficiently to avoid any need to inject additional fuel when operating at or near full throttle, improving real-world fuel economy by up to eight percent. Reduced combustion temperatures also lead to lower risk of uncontrolled combustion (knock) and lower emissions. The reduced knock risk allows the compression ratio of the prototype model’s three-cylinder engine to be increased from 9.5:1 to 11.0:1, optimising efficiency in the low and medium throttle range too, which in turn improve engine power and torque by up to 10 percent.
The benefits of direct water injection cooling can be utilised in various ways. Depending on vehicle type and engine, it is possible to prioritise either increased power or enhanced fuel economy.
The water injection system in the BMW M4 MotoGP Safety Car draws water from a five-litre tank in the boot. Under gruelling race conditions, when the vehicle spends a lot of time operating at full throttle, the water tank is topped up every time the vehicle is refuelled. By contrast, the direct water injection system destined for future production models that is being presented at the BMW Innovation Days never requires topping up in everyday use. Unless the vehicle is operated in exceptional climatic conditions, the system is fully self-replenishing, thanks to on-board water recovery; the water supply for water injection cooling is kept topped up by the continuous recovery of condensed water from the air conditioning system.
Every time the engine is switched off, all the water in the hose system is drained into the tank. This guards against system components icing up in sub- zero temperatures and prevents engine corrosion. The water tank itself is also located in a frost-protected position in the vehicle.