MIRAMAS, FRANCE: As part of BMW’s recent innovation day, we got to sample a host of models showcasing the firm’s future drive technologies. In a departure from the futuristic hydrogen fuel cell and plug-in electric drivetrains on show, BMW also looked to the well-established technology of direct water injection as a means of upping performance while reducing fuel consumption.
We got behind the wheel of a 1,5-litre, three-cylinder 1 Series prototype fitted with BMW’s latest direct water injection system to see just what it can do.
It’s nothing new
Water injection is not a new technology; it has been utilised extensively in aviation to extract more power from engines to reduce take-off distances or quickly gain altitude in a dogfight. It has been utilised from time-to-time in high performance vehicles such as dragsters and racecars, but here BMW sees its latest take on this old technology benefitting the everyday driver.
What’s happening beneath the bonnet?
In essence, direct water injection is applied here to better harness the potential of turbocharging by injecting a fine spray of water into the engine’s manifold plenum chamber and combustion chamber just prior to combustion.
Here it evaporates, cooling the air/fuel mixture to reduce the engine’s combustion temperature by around 25 degrees Celsius. This cooling effect improves combustion efficiency sufficiently to avoid having to inject additional fuel at higher throttle inputs.
In addition to improved emissions and fuel economy, the upshots of this lower combustion temperature include a reduction in engine knock (auto ignition that causes engine damage) that, in the case of the prototype’s three-cylinder turbopetrol engine, has enabled BMW’s engineers to increase the engine’s compression ratio from 9,5:1 to 11,0:1, realising similar efficiency benefits at lower throttle inputs, as well.
Owing to an earlier ignition point (more advanced timing) in the engine’s combustion process, as well as higher boost pressure and the increased oxygen content of the cooled air being fed into the induction system, the engine’s power and torque both receive a shot in the arm to the tune of around 10 %. BMW also claims that this system can help improve fuel efficiency in real world driving scenarios by up to 8%, depending on the model in which the technology is implemented.
Does it work?
The 1 Series 5-door prototype’s direct water injection-fed 1,5-litre turbopetrol unit is based on the 100 kW/200 N.m B38 engine found in the Mini Cooper and BMW 2 Series Active Tourer.
Here it produces around 160 kW and 320 N.m, close to what the i8’s similar three-cylinder unit produces.
On BMW’s Miramas test track we conducted a loop that subjected the direct water injection prototype to different engine loads and speeds ranging from 80 km/h to 130 km/h, and up to 180 km/h, including acceleration and steady throttle input runs.
The engine proved wonderfully flexible and packed more punch, not to mention a smile-inducing burble to its soundtrack, than its diminutive displacement would suggest.
At the end of my run the on-board telemetry showed an average fuel consumption benefit of 2,97 litres/100 km.
Takes a licking, keeps on trickling…
The water feeding the injection system has to come from somewhere, but rather than expensive refills and standing by the garden tap, BMW has taken an innovative approach in keeping the system fed.
In the case of BMW’s direct water injection M4 MotoGP Safety Car, the system is fed water from a separate fillable tank. But the 1 Series’ setup cleverly utilises water scavenged from the operation of the air-conditioning unit. This supply is a) clean, as in distilled by the means of its production and b) means that the system never requires topping up.
On the abovementioned run the track temperature was a searing 34 degrees. With the air-con running in that environment just over two litres of water was produced, comfortably offsetting the amount we burned through on our hard-charging track run.
The tank’s centralised location in the car, along with a line-clearing system that draws water in the feed pipes back into the storage tank ensures that cold temperatures don’t hamper the system’s operation.
Is this the way forward?
Where most fuel efficiency/environmentally friendly technologies reward a softly-softly approach from the driver, the direct water injection system is the polar opposite; operating at its most efficient with the pedal to the firewall.
It’s an interesting solution that could potentially present BMW’s Efficient Dynamics in a different light, appealing to those with a penchant for spirited driving.
Granted, the savings are largely in relation to a foot-flat scenario that will generally use up greater volumes of petrol, but there is the hypothetical potential to piggyback such a system with hybrid technology.
Although there currently aren’t any concrete plans to implement this technology in the medium to long term, it has undergone 100 000 km of endurance testing and development is basically complete and can be quickly deployed if the demand is present.