It’s a miracle! BMW turns water into (engine) whine, CAR+ October 2015 | CAR Magazine

It’s a miracle! BMW turns water into (engine) whine, CAR+ October 2015

Published: 16 September 2015 Updated: 16 September 2015

► Water injected turbo’s for BMW
► M4 GTS concept has indirect water injection
► 3-cyl 1-series, direct and indirect water injection

BMW’s latest technology sounds like snake oil: up to 10% more performance, and benefits to fuel efficiency that increase the harder you drive. But that’s the promise with water injection. Even if you rarely drive flat-out, says BMW, you’ll still get results. To prove the point, it’s being demonstrated at polar ends of the line-up: ultra-efficient three-cylinder 1-series and ultra-powerful M4 GTS concept car, which use different versions of the technology. We took a look at BMW’s Miramas test facility…

1) Water injection, distilled

Water injection is not new. It’s been used in turbocharged rally cars for years, and aftermarket kits filtered into the performance-tuning industry well over a decade ago. But the benefits to improving mpg have long been known. Why only introduce such a simple, cost-effective technology now? Because it’s perfectly suited to turbocharged petrols, and BMW has gradually switched to forced-induction since 2006’s 335i. Now every petrol BMW has a blower.

2) Coming on stream

The system in the M4 GTS is production-ready. Water generated by the air-con is pumped from a seven-litre tank and injected into the intake manifold plenum (indirect injection). When the water vapourises, it cools the intake air like a second intercooler. BMW quotes a 10% performance boost, but it’s the fuel-efficiency claims that really stand out: mash the throttle on track and there’s a promised 23% improvement in mpg.

M4 GTS concept has indirect water injection. Production version gets it in 2016

3) The next wave

Further from production is the three-cylinder 1-series. It uses both indirect and direct water injection, water being injected straight into the combustion chamber for the latter method at a rate of around 30% to the amount of fuel. Once injected, water evaporates and cools the 100oC-plus combustion chamber by around 25oC. This reduces the chance of ‘knocking’, so the compression ratio can be ramped up from 9.5:1 to 11.0:1, improving low- to medium-throttle efficiency. There’s only a 2-3% improvement in lab tests, but that rises to 3-8% in typical driving. And the extra power and full-throttle mpg benefits seen on the M4 GTS are retained.

4) Water-tight logic

When the engine is turned off, water in the pipes drains back into the tank, preventing icing in sub-zero temperatures, and engine corrosion. BMW says it should be unnecessary for 80% of drivers to ever re-fill the tank, only very hard driving or exceptional temperatures dictating otherwise.

By Ben Barry

Contributing editor, sideways merchant, tyre disintegrator