Bosch has developed a new technology that uses water injection to reduce fuel consumption by 13%. The system, which featured for the first time in the new BMW M4 GTS, sprays a fine vapour of distilled water into the intake duct, offering significant power and efficiency advantages in real-world driving.
According to Bosch, a modern combustion engine currently wastes around a fifth of its fuel, because it is used to cool the engine before combustion. Cooling the engine reduces knock, which delivers greater power, but doing so with fuel is highly wasteful. Bosch’s new technology replaces this with water; before the fuel ignites, a fine mist of water is injected into the intake duct. The water’s high heat of vaporisation provides effective cooling, meaning that fuel is only used during the combustion process.
The fuel economy gains offered by water injection is greatest in the three- and four-cylinder downsized engines, which are most commonly found in typical mid-size cars. In the new fuel consumption test that comes into force in 2017 (WLTC), water injection makes it possible to save up to 4% of fuel. In real driving conditions, fuel consumption can be reduced by up to 13% when accelerating quickly or driving on the motorway.
Water injection can also make cars more powerful, delivering an extra boost for turbocharged engines. Advanced ignition means that the engine operates even more efficiently, allowing engineers to extract additional power.
“It has never been more important for vehicle manufacturers to extract every element of real-world fuel efficiency from the engine,” explained Arun Srinivasan, head of Bosch Mobility Solutions UK. “With water injection, we have identified a highly effective way to make major efficiency gains without changing how the owner uses or maintains the vehicle.”
Water injection only requires a very small volume of water, meaning the compact water tank that supplies the injection system with distilled water only has to be refilled every few thousand miles at the most. If the tank should run empty, the engine will still run smoothly but with lower torque and higher fuel consumption. The water also evaporates before combustion happens in the engine, meaning that there is no risk of the engine rusting.