PH Origins: Water injection
Engine knocking at high boost levels? Time to sling some water down its throat. No, honestly...
Introducing a small and controlled quantity of water into an engine's intake system, however, can result in significant benefits - primarily by reducing the chance of detonation. This process, also called 'knocking', occurs once combustion has started and when temperatures and pressures in the cylinder get too high. This can cause the remaining fuel to self-ignite and burn in a rapid, uncontrolled fashion that results in a pronounced rise in pressure.
Detonation will reduce power, as it's not an efficient means of burning the mixture, but it can also cause significant damage to the engine's components if left unchecked. Feeding water into the engine's intake manifold, however, cools the incoming charge - which lowers the temperature in the cylinder, reducing the chance of detonation. When combustion starts, the water is converted to steam - a process that absorbs energy - and this further reduces peak temperatures and the occurrence of detonation.
The concept is by no means a recent development, with references to 'internal cooling' by water injection dating back to around 1900. It was then exploited during World War II, granting higher boost levels and reducing the chance of terminal detonation in force-fed aviation engines. It even outlived the introduction of the jet engine, as it was discovered that its use could cut temperatures and boost thrust - by increasing the mass moving through the turbine - when required.
Water injection is also particularly useful in turbocharged cars, where cylinder pressures and temperatures can easily reach excessive levels. The high-performance, twin-turbocharged BMW M4 GTS, unveiled in October 2015, was one such car that benefitted from a water injection system. BMW stated: 'It relaxes the thermal constraints on power and torque, and has already proved itself on race tracks around the world'. BMW also claimed that the M4 GTS was the 'first production road car fitted with such innovative technology'.
The upgrade pack even included a subtle 'S' badge for the rear of your Saab, with the fitting instructions requiring you to 'loosen the 900 turbo emblem and move it a bit to the left' to create the necessary space. Some cars were even fitted with water injection as standard, including the rare 1980 Saab 900 Enduro - an Australian market special edition.
The Swedish solution also dispensed its water in front of the turbocharger and used the compressor wheel to atomise the water before it was ingested by the engine. This caused the compressor to erode over time. BMW avoided this problem by using a series of precise high-pressure injectors that spray a fine mist into the intake after the turbocharger.
The system was much needed, too, as the boosted V8 - destined to later be reinvented in naturally aspirated form as the Rover V8 - packed a then turbo-unfriendly compression ratio of 10.25:1. The 'Turbo-Rocket Fluid' used was effectively a 50/50 mix of distilled water and methanol; the water served primarily to cut temperatures and detonation, while the methanol increased the cooling effect of the mixture, served as additional fuel and protected against freezing.
All of this additional complexity and cost, and myriad engine-related developments, have resulted in water injection remaining relatively uncommon in production automotive applications. That said, aftermarket systems are popular in performance turbocharged petrol and diesel applications - with myriad companies, including Snow Performance, AEM, Aquamist and Nitrous Express offering various water and methanol injection set-ups.
And was very quick
The guy across the road had an H.E. Jag XJS and it’d easily pull away from that going uphill out of town, as they both had lots of fun finding out.
. (Mind you, said neighbour also had an RC30 - so he’s a star in my book forever!).I learnt to drive in it (explains a lot - probably), but couldn’t get insured on it as a newly passed driver. I guess insurance companies aren’t that stupid! I remember that people used to try all sorts of shenanigans upon coming up to the back of the car in a 30 - and would position themselves ready to “go” when we hit NSL, to invariably have to pull back in, as we’d have disappeared up the road. Had lots of gobsmacked people asking WTF at the next junction, etc - as the mk2 Uno didn’t have any badging on the back by way of giving performance away - most people saw a learner Uno and assumed it’d be slow & pottering about - I have never driven like that...
It pottered on for a good few years (was over 100k miles with no engine issues) surprising all manner of stuff, before being half-inched one afternoon in E15, and was never seen again.
Water injection in jets is well known, the Harrier has a tank for distilled water behind the engine - a fifty gallon water tank. Lasts about five minutes when hovering.
Never tried it, unsurprisingly, but I often wonder if anyone ever did.
The new WLTC and RDE tests are testing the engines at much higher loads than before. The previous strategy was to go rich at high load to reduce the turbo inlet temperature, now this is not allowed a new method to cool the exhaust is needed. Hence water injection is likely to be quite common on engines >90kW/L.
The alternative is higher materials specs for the turbo which will be very expensive.
The effect on detonation is fairly minor as the engines are already using direct injection an having less issues because of it.
I'm currently toying with the idea of running meth on my stage 2+ Golf R, its quite a common upgrade for the TFSI engines as it keeps the inlet and valves clean from the common carbon build up that plagues these engines, keeps the engine running clean and cool and I'm hoping for maybe 5% extra power too
The new WLTC and RDE tests are testing the engines at much higher loads than before. The previous strategy was to go rich at high load to reduce the turbo inlet temperature, now this is not allowed a new method to cool the exhaust is needed. Hence water injection is likely to be quite common on engines >90kW/L.
The alternative is higher materials specs for the turbo which will be very expensive.
The effect on detonation is fairly minor as the engines are already using direct injection an having less issues because of it.
(Good article btw)
Water injection in jets is well known, the Harrier has a tank for distilled water behind the engine - a fifty gallon water tank. Lasts about five minutes when hovering.
https://en.wikipedia.org/wiki/BMW_801#801D-2_and_8...
Interesting that they also had to revert back to the water-methanol injection rather than injecting more fuel to cool the charge. Although it was down to a fuel shortage rather than emissions regs...
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