| Issue: 478 | Section: Technical Features | 5 May, 2008 |
AutoSpeed Water Injection System Part 1A straightforward but very efficient water injection systemby Julian EdgarClick on pics to view larger images |
|
|||
|
At a glance...
|
|
|
|
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 emissions.
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.
Our System
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 systems.
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 parts shop!
The Pump
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 high pressure.
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 battery!
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 near-continuously.
To cater for continuous running applications, we have developed a fan cooling system for the pump – more on this in a moment.
Power Supply
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.
Pump Cooling
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 pump.
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 Nozzle
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 atomise water.
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 |
Flow | |
|
(ml/minute) |
(litres/hour) | |
|
|
|
|
|
0.30* |
35 |
2.1 |
|
0.60 |
65 |
3.9 |
|
TN 1.5 |
145 |
8.7 |
|
TN 2 |
170 |
10.2 |
|
TN 3 |
230 |
13.8 |
|
TN 4 |
260 |
15.6 |
*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.
Nozzle DisassemblyThe 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. |
Filter
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 straight in.
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 whole operates.
The Parts
|
| 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! |
Share this Article:
|
|
|
|
|
|
Copyright © 1996-2008 Web Publications Pty Limited. All Rights Reserved |
