t is the first attempt of explaining how different type of systems work and its advantage and dis-advantage, based on current systems offered.

1) Single-stage
2) Two-stage
3) PWM Pump controlled system
4) PWM Valve controlled system
5) System that will integrate well with third party controllers.
6) Direct port




The single stage WAI (water alcohol injection), as the heading implies, is not as basic as most people expects. It some cases, it will out perform a two-dimension progressive system. Please do not underestimate it. I will try to explain briefly why after the next few paragraphs.

Having a single trigger point and a fixed flow rate, one will get to know its effect on your engine very quickly. Due to its consistent repeatability, it is very easy to tune. This type of system is normally set to start spray in the peak torque region, where the engine is most likely to knock.

As the RPM climbs, the ratio of water to mass air tends to decrease. This may not be a bad thing because the tendency to knock is also lessen as the wastegate starts to open and prevent the boost pressure from increasing further. The volumetric efficiency of the engine also decreases as RPM climbs, breathing in less air. This also has the effect of reducing the engine's tendency to knock, demand of WAI flow is less. Unfortunately some engines do require continuous WAI flow at higher RPM due to heat build up through friction and turbo efficiency.

A 2-D pump speed system based on manifold pressure is a little bit tricky to tune compared to the single stage system. The user has to set the start and finish pressure points, those points are sometimes set at a considerable distance apart. Matching those operation points in a 3-D environment such as RPM/Boost ramp (nonlinear) is quite difficult. We will be discussing it in more details later.

FOR:
1) Low cost, simple and dependable.
2) Easy to tune
3) Very effective on a stock factory set up with a few pounds of boost extra.

AGAINST:
1) Dynamic operating range is narrow, may not be as effective on a high RPM knock suppression.
2) For high power/ high % alcohol applications, considerable fuel has to be taken out (boost clamp) to make the afr tolerable. Some sort of failsafe mechanism is necessary to prevent engine destruction when the WAI fails to delivery the correct flow.



The 2-stage system
(13th November 2006)


At present, adding a second manifold pressure switch to active an additional solenoid valve at a higher manifold pressure is the definition of a 2-stage system.
This arrangement gives the system greater flexibility as well as extending the flow range. It addresses the problem associated with the single stage system, too much flow at the start and not enough when RPM climbs beyond the wastegate setting.

As the system is based on boost trigger, it still won?t address the RPM related flow. For a turbo charge engine, the most significant active regions are the boost ramping stage and engine?s maximum torque range. A two-stage system fits these two regions nicely, allowing the some form of cooling demand during the ramp-up stage. The second stage provides the in-cylinder cooling and knock suppression as the engine is under the most stress or highest BMEP (Brake Mean Effective Pressure).

FOR:
1) Relatively low cost to give mark improvement to the single-stage system.
2) Provides well defined triggering points during the boost cycle.
3) Minimising the under/over flow problem.

AGAINST:
1) Trigger points requires some time to set up.
2) Triggering points may differ on each gear if you have a fast spool up turbo
3) Require a bit more care during tuning

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(18th November 2006)


Does the pump speed controller perform better than a two-stage system, you are about to find out.

Changing pump speed merely put more pressure behind a nozzle, hence more flow. This type of system is commonly known as a progressive system (pump-speed).

Let us examine how much a M5 nozzle will flow between 40psi to 160psi. According the chart below (Published by Hago, a well know US oil heater nozzle manufacturer), the flow starts from 200cc/min and ends at 400cc/min., when pressure is increased from 40psi to 160 psi.



Almost all PWM pump controller on the market uses Shurflo pump, designed to operate between 0-150psi. The heart of the system is an electronic motor speed controller, vary the speed according to a sensor. It could be a MAP sensor, a MAF or any sensors that read engine load. It is normally a 2-dimensional system. A manifold-pressure type system does not take into account of any RPM change.

A swirling type atomising nozzle requires a head pressure of at least 30psi to produce a decent mist. Droplet size is very important to the inlet cooling ability and even cylinder distribution. Let say the system pressure starts at 40psi (as shown on the chart) and ends at 160psi. One can assume you will get a 4x flow range? In practice, not so, according to the chart, you will only get a flow change from 200cc/min to 400cc.min (see M5) instead of 200cc/min to 800cc/min. Flow/pressure obeys the square-root law.






Being "progressive" implies a reasonable dynamic range between start and finish. How progressive? Almost no one ever questions this. Most people just assumes it covers all the flow requirement between 10psi to 20 psi of boost once the range-dials are set on their pump speed controller. In practice, you cannot expect the same M5 nozzle will serve a wider operating range between 5-25psi by merely changing the dial, the range is governed by the law of physics and not a technically advanced motor speed controller.

If one would want to delve deeper into the subject, as the title demands. So the subject will continue?

Just to recap, good dynamic range (pressure/flow span) is the main factor one should expect from a "progressive" WIA system. Let see what a 150psi system can really offer. We shall take into account of the effect of manifold pressure, inline checkvalve as well as minimum pressure for a good atomised spray.

For example:
1) Manifold pressure start: 10psi
2) Manifold pressure ends: 20psi
3) Inline checkvalve crack pressure: 30psi
4) Minimum pressure of the atomising nozzle: 30psi.

When the system starts: it will instantly see an initial back-pressure of 60psi and a final back-pressure of 70psi (extra manifold pressure). The actual dynamic pressure range is now from 60psi to 110psi. The system can now only manage a 35% change in flow, far from one would imagine a 150psi pump system should perform.



There are other factors that could also affect the performance of the 2-D progressive pump system. It may be a subject for a later discussion, depending on the interest of the readers. Chart below is a predicted performance of a progressive system compared to a single and two-stage system. I hope there will be people chiming in to add to this. At first glance, it doesn't appear there is a distinct advantage for adding a progressive controller. Adding a bigger nozzle doesn't alter the dynamic range, it just shifts the whole curve higher.







FOR:
1) Easy to set the start and end point.
2) Some correlation between manifold pressure and flow

AGAINST:
1) Limited dynamic range, system becomes less effective after wastegate pressure.
2) Extra cost can easily be used for a higher performance two-stage system with greater dynamic range .
3) If the 2-D system is used to replace high % fuel with alcohol, re-mapping the 3-D fuel map will be very difficult due to the wide dynamic flow range demanded by the engine.

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NEXT: PWM valve system will follow. Please chime in with more comments on the above systems and help to build up the above information with more practical experience. I will continue to update this page until we have covered all the other controllers.

 

my compliments on an excellent post dealing w the fundamentals of AI delivery.

the key is that flow varies w the square root of the % change in pressure. increase pump pressure 4X, flow increases 2X.

also, in the last graph the delivery line is a RATIO so the fact it is declining does not mean that less injectant necessarily is being offered, but less in relationship to fuel.

as we currently attempt to tailor AI to pump w progressive controllers and we construct all kinds of slopes do keep in mind that pumps are mechanical things and have momentum and mass and are not capable of responding like an electronic (say fuel injector) valve.

all this does not mean that progressive controllers are a bad thing. i currently run one and am ecstatic as to what i accomplished in 06. you just need to find a curve, consider it to be a constant and tune around it w pump.

by doing this you can run 25 psi boost v 14 psi boost. is it a work of art as an electronic valve controller/fuel injector would be? nope. but it is what we have today and it works.

Richard is on to something big for 07 and is correct as to the workings of our current delivery systems. as he says, do not discount them as they do work, but something very neat may be on the way.

thanks Richard. your post above is a major asset to out AI section.

howard coleman

 

Howard,

Thanks for pointing out the flow decline is in % relationship to power/fuel/rpm. The actual flow is the same for the single stage.

For the progressive pump system, the flow decline only happens when the boost ceased to climb after wastegate setting. I haven't plotted for further flow decline if there is a drop in boost at higher RPM. (under size turbo charger has this effect)

These alcohol % deline can easily be compensated by re-mapping the fuel injector. But not so easy if you run M50:W50.

We don't have anything particularly special to offer on the IDC, just adding a big pump to ensure the water/alcohol does not fall short for those 100% alcohol users, In general, you need to inject 2.5x times of methanol to water to arrive at the same cooling capacity.

There is a also a significant price advantage by using the Shurflo pump. But still cannot complete against systems with their pump with a lower wattage motor. We are getting there slowly.

Richard

 

Wow, that’s a lot to think about, especially for Mr. newB like me. I was leaning towards a PWM Pump controlled system because I didn't want to inject max water when I'm boosting at 6psi (10psi max) at 50% throttle. For turbos that have almost no lag like mine, that really seems like the only benefit above a Single-stage system. I think a lot of this needs to talk to the two types of users. One is like Howard that tunes for AI. The other is like me that buys a kit to protect against detonation without tuning for it. In this situation too much water could bog the engine from what I have been reading.

Well those are my semi-uneducated random thoughts. I look forward to the next segment!

 

Top thread richard. It explains perfectly how the current crop perform.

Scott

 

In internal combustion engines, water injection, also known as anti-detonant injection (ADI), can spray water into the incoming air or fuel-air mixture, or directly into the cylinder to cool certain parts of the induction system where "hot points" could produce premature ignition. In jet engines it increases engine thrust at low speeds and at takeoff.

Water injection was used historically to increase the power output of military aviation engines for short durations, such as dogfights or takeoff. However it has also been used in motor sports and notably in drag racing. In Otto cycle engines, the cooling effects of water injection also enables greater compression ratios by reducing engine knocking (detonation). Alternately, this reduction in engine knocking in Otto cycle engines means that some applications gain significant performance when water injection is used in conjunction with a supercharger, turbocharger, or modifications such as aggressive ignition timing.

Depending on the engine, improvements in power and fuel efficiency can also be obtained solely by injecting water.[1] Water injection may also be used to reduce NOx or carbon monoxide emissions.[1]

Water injection is also used in some turbine engines and in some turboshaft engines, normally when a momentary high-thrust setting is needed to increase power and fuel efficiency.

 

If the engine isn’t heavily modified, and kept at near stock boost...
*Tuning with AI isn’t mandated and single dimension system is appropriate...IMO. Anything more sophisticated is over-kill...IMO.
*A single dimension system means fewer components with fewer failure points.
*Components can be purchased inexpensively in a ‘kit’ OR ala carte, and from the same or different vendors.
*Fail-safes can be as simple as a float sensor in the tank to signal refill time, and some signal when the pump goes on-line.