BMW reveals water-injection tech

BMW has promised to deliver higher horsepower and lower real-world fuel consumption at the same time by squirting water into its engines, and it's invited us to test the ground-breaking new technology.

The Bavarian car-maker is actually planning to use the technology on all of its turbocharged petrol engines, eventually, which means all of them because BMW no longer makes a naturally aspirated petrol engine (unless you count the range-extender in the i3).

BMW has turned to injecting water into its engines because, unlike diesel engines, there’s a limit to how much turbo boost you can use on a petrol motor before you heat the combustion chamber so much that you risk knocking (uncontrolled fuel detonation). And knocking is bad news.

We were invited to test a prototype at BMW tech day in Maramas, France this week, but it isn’t the first water-injected BMW prototype. Far from it. In fact, BMW has been testing one in public for some time in the M4 that follows the first lap of the MotoGP field, though that’s a generation behind this one in both technology and philosophy.

This 1.5-litre three-cylinder turbocharged 1 Series benefits from using the MotoGP M4’s system, which injects water indirectly into the inlet manifold and it injects water directly into each combustion chamber.

Either way, the idea is to lower the temperature inside the cylinder, which lets BMW use higher compression ratios and more boost pressure, which tantalises with the theoretical benefit of using less fuel on full throttle.

As it sits here, the 1 Series prototype manages to lift power from 150kW to 160kW, while the torque peak jumps from 280Nm to a not inconsiderable 320Nm. All from the same capacity and with the peaks arriving at the same engine speeds. Its compression ratio has jumped up from 9.8:1 to 11:1.

BMW is determined to swing water-injection into widespread production.

“The topic of water-injection is presented here, and the injection directly into the cylinder is very important to me,” BMW’s board member in charge of development, Klaus Fröhlich, said.

“We are going to continue with this in all variants in different drive systems, just as variable valve timing became normal in all variants.”

Before we begin, then, a little on how it works from BMW’s head of current projects and applications for petrol engines, Werner Maehrle.

“If you operate a petrol engine under high load, we have to reduce either the pressure or the temperature to reduce knocking. This also means we lose efficiency, so we use more fuel than we need to use.

“Water-injection physically means cooling the fuel-air mixture into the combustion chamber. It’s injected into a very fine spray that cools the mixture but the water is evaporated completely before the combustion phase.

“We have to get the water into the combustion chamber in a very fine spray. If you’re using full throttle, we need to get it in there at a ratio of about 30 per cent water compared to the fuel you have in there.”

That all sounds simple enough, right?

Well, key supplier Bosch still isn’t sure, because BMW’s direct-injection water system asks its fuel pumps and injectors to accurately meter and deliver precise volumes of water into the cylinder as well as petrol.

And BMW admits Bosch isn’t yet chuffed by its ability to guarantee pump longevity in production. But the direct injection system isn’t in production yet (though the M4’s indirect injection system, which uses its own water pump, is much closer to production).

The guinea pig of a 1 Series sits in front of us, loaded to the gills with computer equipment and the standard development engineer-spec robust laptop computer.

It’s only a 4km oval test loop, but that’s enough for Maehrle’s guys to gather some critical data to show the differences between this and the stock three-cylinder, which uses variable valve timing and lift, plus direct fuel-injection.

There’s no difference at idle whatsoever, because the system isn’t needed at idle and it only works on demand.

It moves off freely and cheerfully and feels, if anything, slightly crisper in its delivery than the standard version. Maehrle explains that it doesn’t need to retard its timing, plus it gets more out of less petrol.

The little three-pot sounds and feels willing and smooth and, even though it does its best to sound like a four, there’s enough of the three-cylinder character that comes out.

And it’s lively. It doesn’t matter what speed you’re doing, mash the throttle and the 1 Series responds rapidly and enthusiastically. It’s like the car is suddenly carrying 200kg less mass around with it.
There’s a responsiveness that the standard car doesn’t quite have, too, and it even feels smoother most of the time.

And it’s definitely quicker in the mid-range, but it’s also quicker if you swing the tacho all the way up to its redline over and over again.

BMW has taken a good engine and made a great engine. Well, that’s what it’s done with a prototype, anyway, explains Maehrle.

“The fuel consumption under full load is reduced in comparison to a series engine, via combustion efficiency and the adjustment of the fuel-air mixture.

“We can reduce the charge pressure, too, to have the same output. If we use the same pressure we increase the performance. It’s a very simple ratio.

“In the real world, the average customer can reduce the fuel consumption about three to eight per cent and you get a five to 10 per cent increase in efficiency. It improves the entire area of the torque and power curve.

“If you compare it to other ways of reducing consumption, the normal driver has a higher rate of fuel saving.”

On our short drive, during which the horses were not spared, the comparative benefit compared to the production 1.5-litre motor saved 2.57L/100km (or 19.1 per cent) according to BMW’s computer analysis. And they tested the production 1.5-litre engine to death here, so we’d place a fair bit of faith in that.

And, if you worry about how you’d keep enough water in the car and what a pain it will be to fill it with water every time you fuel up, the prototype used 0.04 litres of water over 4km – so 0.01 litres for every kilometre. On the flipside, it actually generated its own water at the rate of 2.1 litres an hour. Err, what?

“We get the water from air-conditioner condensation,” Maehrle explained, “And it’s hot today. Normally, that condensation drops on the street but it’s very suitable for using in an engine.

“The amount of water you get depends on the humidity, but based on our calculations, 80 per cent of customers will never have to refill the water.

“For them, the water we take from the air-conditioning and from a container in the engine bay (prototype systems vary between five and seven litres) that’s large enough to sustain it for 18,000km a year or more.”

And if that isn’t enough (highly unlikely, given Australia’s usual rates of air-conditioner use), you can top up the system’s water tank with bottles of distilled water.

That leaves the tricky question of why nobody else does it in production today – which largely boils down to fire and water not being traditional buddies.

“The high-pressure fuel pump mixes the fuel and water before the injector nozzle and it becomes an emulsion and then it is injected into the combustion chamber in a liquid state,” Maehrle explained.

“The injection is in the suction phase and it has to be vaporized inside the cylinder before the combustion begins. On full load, there are two injections per stroke of petrol, but mostly there is just one, and it can operate at ratios of between 10 and 30 per cent, depending on the load.

“The main point we are looking for is the temperature at the end of the compression stroke when you begin ignition. This temperature is usually around 400 to 500 degrees Celsius, and with the direct-injection water system we can reduce that to 330 degrees. The delta is 70 degrees of difference.

“For the engine, it’s like driving on a cold winter’s day, all the time. This has a significant affect on the knocking behaviour.”

And, when you do end up driving on a cold winter’s day, the system knows when it’s too cold and switches off. Not only that, but it drains all the pipes and valves and injectors of water to stop it freezing. And if the water container itself freezes, it is heated so quickly that the system is always available when it’s needed.

And while it’s needed on hard acceleration, it’s not needed much when the car’s at idle or cruising, so the injectors just pump in fuel and the valves let in air. Just like they’ve always done.

“It has a very small effect on NEDC [fuel consumption], but it has many advantages over the entire range of the engine.

“You would need the water injection for sharp acceleration and not for cruising. Whenever you operate the gas engine to get high power or high torque, you will use it, and it’s an advantage.

“Also it’s useful on hybrids when you charge up the batteries,” he said.

So if a special-edition M4 will be first with the early, indirect-injection version of the system later this year, followed by direct-injection later and, in all probability, a combination of both technologies even further down the track, which BMWs will be first?

“The cars with the biggest specific power outputs benefit the most, but everything with a turbo will benefit,” Maehrle said.

“But I don’t want to pre-assume that this is the only system that will work but it was fastest way for us to get it into this test car.

“The three-cylinder prototype has the indirect system along with a direct-injection system. The two can run together or separately, as the situation demands.

“When the time comes, we have a time frame for direct-injection and it’s a time frame that depends on management to decide which model will get the first production system.”

Unfortunately, the decision has not been made just yet.