If you’ve read our recent two-part series on water injection (see The H2O Way Part 1 and Part 2) you’ll know that there is excellent engineering
evidence that water injection raises the effective octane level of a fuel,
allowing higher forced aspiration boost pressure, and /or advanced ignition
timing on both forced and naturally aspirated engines. It also keeps the engine
internally clean and can result in more power, better fuel economy and lower
In short, it’s good stuff.
But almost any enthusiast you’ll ever meet is dead-set against water
injection, considering it to be an inferior band-aid solution for major tuning
errors. But that’s simply bunkum; some of the best engineers of the last century
are not wrong!
The problem has largely been that after people think ‘water’, ‘spray’, ‘car’,
their minds immediately turn to windscreen washer pumps and crude nozzles. So no
wonder their systems are ineffective at atomising water, stop at all the wrong
times and unexpectedly run out of water!
Older readers may also remember the systems that used manifold vacuum to suck
water into the intake manifold through a small jet. Wild claims (especially for
fuel economy improvements) were often made about these systems, again reducing
the credibility of water injection in the minds of the public.
But over the last few years some much more sophisticated water injection
systems have started appearing. These use high pressure pumps and are sometimes
electronically mapped. However, these systems can cost so much that people are
wary of adopting them.
We have been investigating water injection systems for a long time. That
investigation has included the collection of technical and engineering papers
that date from the 1930s to today (some of that material was used in the series
cited above, including coverage of the jet engine system shown at right), and building both boost pressure and pumped water injection
The system that we’ve come up – while nowhere near as cheap as a windscreen
washer pump and nozzle – works well, atomising the water to a very fine spray.
Depending on how you assemble it, it will cost about AUD$300 – far less than
some professional systems using inferior components. It can also be configured
as a roughly proportional system, adding more water when loads are greater and
less when loads are lower.
If you’re a longstanding reader, you will have seen much of the following
system before. We first presented it as a very efficient intercooler water
spray, something at which it is brilliant.
Firstly, an overview of the components – and you don’t need to go to an auto
The heart of this system is the pump – and what a pump it is! For years we’ve
been looking for a really good ultra-high pressure pump that will cope with
water. Fuel pumps won’t – they corrode internally. Multi-diaphragm pumps (as
used in boat and recreational vehicle potable water supply systems and most
aftermarket water injection systems) can generate good pressures (eg 60 psi) but
they’re expensive and noisy.
We’ve even looked at the Aquamist water injection pump; it’s an absolute
leader in high pressure, low volume 12V water pumps – but the huge cost has
always put us off.
But it’s the Aquamist pump that sent us off in the right direction. Rather
than using rotating rollers (like a high pressure fuel pump) or diaphragms
compressed one after the other (like a diaphragm pump), the Aquamist pump uses a
pulsating piston. The piston, powered by an electro-magnet, slides back and
forth, pushing ahead of it little bursts of water that soon add up to a very
And guess what? Just the same design of pump is used in espresso and
cappuccino coffee machines! Except instead of costing mega-bucks like the
Aquamist pump, you can have your very own Italian-made Ulka vibrating pump for
AUD$107! (And if you live in Italy , probably for one-third of that.) So that it
can be used in coffee machines around the world, the Ulka pump is made in 110V
AC and 220V AC models. But hold on, what about using it in cars? Well, because
of the technological advances made in recent years with mains power inverters,
for just an extra fifty Australian bucks you can power it straight from the car
Under AUD$160 for a durable pumping system capable of over 15 Bar (218 psi) –
and actually designed to pump water?! You can see why we’re excited.
Here are the manufacturer’s performance specs for the Ulka E5EX pump. As can
be seen, flow drops off with increased pressure - but this means that you can
control the flow of the pump just by changing nozzle size... and the pump
doesn’t get overloaded. The curve also shows it’s possible to flow over 200cc a
minute at a pressure of 10 Bar (145 psi) and 100cc a minute at 15 bar (218 psi)!
When measured, the pump did even better than this, with a peak recorded
pressure of 25 Bar, or 360 psi!
These performance stats are just stunning. Why? Well, generally, the higher
the pressure you can run, the smaller will be the droplet size coming from a
high quality nozzle. We’re getting ahead of ourselves a little, but flowing a
low volume of water at a very high pressure is exactly what you need to produce
the smallest drops.
In addition to its very high pressure, the Ulka pump has another attribute –
it can provide enough suction to draw up water from a reservoir mounted below
it. This feature gives greater flexibility in pump mounting position.
However, the Ulka pump does have one shortcoming.
In its normal coffee machine use it is designed to run for short periods,
rather than continuously. If the pump is run continuously, it will get very hot.
In most water injection applications (eg on a turbo petrol engine) the water
injection system will not need to run for very long at a time. For example, in a
burst of boost up to the speed limit, the system might only be spraying for
seven or eight seconds. However, in a diesel turbo engine, the length of time
the system needs to continuously operate is likely to be much longer. And, if
the system is used in cruise, it will need to run at times
To cater for continuous running applications, we have developed a fan cooling
system for the pump – more on this in a moment.
As mentioned above, the Ulka pump needs an AC high voltage power supply to
operate. However, it draws only 50 watts and so pretty well any 12-240V inverter
will work the pump. We selected one from Dick Smith Electronics – it cost
AUD$49. It provides up to 150W continuous and 300W peak – far more than required
in this application. Further, the inverter includes low voltage,
over-temperature and short-circuit protection.
As described above, when the pump is continuously used for long periods, it
gets hot. There are two ways in which we can reduce the heat build-up in the
The first way occurs automatically when the pump is run from the Dick Smith
Electronics inverter. Inverters are designed to turn 12V DC into 240V AC (or
whatever the mains power voltage is in your country). Mains power AC has a
waveform that looks like a sine wave, whereas cheap inverters tend to churn out
a waveform that’s more like a square wave.
The interesting thing is that the Dick Smith Electronics inverter (and
probably most others) has a square wave output that has a duty cycle of less
than 50 per cent. Without getting too complex, the heating in the pump depends
on the duty cycle and since it’s less than 50 per cent, the pump stays cooler
working on the inverter than it does working on ‘proper’ mains power.
However, when run for long periods (eg 15 minutes continuously) the pump
still gets too hot. To overcome this problem, we housed the pump in a metal box,
cut large holes top and bottom and ran a 12V PC-type fan on the box. This draws
air from the box - and so from around the pump. The box we used is Jaycar
Electronics cat no HB-5444 and the fan (and fan grilles) we’d previously
salvaged from discarded equipment.
Soft polyurethane collars were used to mount the pump, so reducing vibration
transmitted to the box.
Together with the water flow through the pump, the fan cooling is
sufficiently effective to allow the pump to run continuously.
The Spraying Systems Company of the US make amongst the world’s best water
spray nozzles. They’ve got a huge range of nozzles, including those designed to
The nozzles used in this application are in the Unijet small capacity range.
These assemblies consist of a ¼ inch TT male body spray nozzle holder, a screen
strainer incorporating a check valve, a spray tip and a tip retainer. All the
components are top quality brass, with the nozzle tips using a stainless steel
insert. The check valve stops the valve from dribbling when the pump is
off (even if the nozzle is located below the level of the pump) and the strainer
stops the tip being blocked by foreign material that might be contained in the
water (however, see below for more on water filtration).
Used with the Ulka pump and DSE inverter at 13.5V input, the following
measured spray volumes are achieved:
¼ inch Tip Size
*only just atomising
Note: the factory nomenclature used for these tips can be confusing. Please
check carefully before ordering.
If you need a larger flow, we suggest you use multiple nozzles.
The nozzle assembly (including strainer and cap) costs AUD$12 and the
precision nozzles are $21 each.
It’s possible to get barbed hose fittings for both the nozzle and the pump
and connect them together with high pressure hose held on with hose-clamps.
However, we found in bench testing that time after time, the hose would blow-off
either the pump or nozzle – we’re talking high pressure here!
You may be able to get away with running two hose-clamps at each end but to
ensure reliability, we chose instead to use ‘push-in’ fittings for hard plastic
hose. Good hydraulics and pneumatics hose suppliers have these fittings (and the hose).
The feed hose to the pump handles effectively no pressure and so pretty well
any hose can be used.
The Spraying Systems nozzles described here can be disassembled. When you
remove the tip and look in the back, you’ll see a screwdriver slot. If the tip
is held (eg between blocks of wood in a vice) the insert can be unscrewed. This
is particularly useful if the nozzle has been contaminated with very fine dirt
particles. Without pulling apart the nozzle, it’s near-impossible to get the
finest dirt out.
Despite the fact that the nozzles have their in-built mesh filters, if you
use the smaller nozzle sizes it is vital that you use an additional filter in
the system. (The mesh insert behind the nozzle is designed to catch only
relatively coarse particles and the nozzle will become blocked if further
filtration isn’t undertaken).
The filter we used is designed for fridge drinking water systems. It’s a
universal replacement part for a range of fridges and comprises a cylinder about
280mm long and 70mm in diameter. It’s rated to 125 psi but we placed it on the
suction side of the pump – the pump can easily draw the water through the
filter. The filter was purchased on eBay for AUD$21.
It has threaded ends allowing normal brass barbed hose fittings to be screwed
Important note: this filter needs to have about 18 litres of water flushed
through it before first use.
OK that’s it for the hardware. Next week we’ll look at how the system as a
Ulka E5EX coffee machine pump
In Australia, Jumbo Coffee on 02 9666 6114
12 > 240V AC 150W inverter
Dick Smith Electronics
Spraying Systems Unijet ¼ inch TT male body spray nozzle holder, screen
strainer, spray tip and a tip
In Australia, Spraying Systems on 03 93180511
Cartridge fridge water filter
Assorted plumbing fittings
Specialist pneumatics/hydraulics supplier
Footnote: a reader has pointed out that the Ulka pump is available even more cheaply at http://www.espressoworkshop.com/shop/shop133.html - in fact, just AUD$66!