On J230, the heat, and suitability of the Rotax 912ULS

[facthunter]

The volumetric Efficiency will be way under 100%. You are only putting out about 30 HP/ Litre at cruise. Nev

[Bruce Tuncks]

Thanks Nev, and you are right. But that correction will leave even less air to be cooled so the new figure will be worse.

[aro]

16 hours ago, Bruce Tuncks said:

Here's how I got the 55 l/sec. A 2200cc4 stroke sucks 1100 cc/rev and 3000 rpm= 50 revs/sec. So the engine sucks in 1.1times 50 =55 litres/sec.

You didn't use 55l/sec in your original calculation. You used 5.5l/sec.

 

16 hours ago, facthunter said:

The volumetric Efficiency will be way under 100%.

True, but it gives a reasonable point to start from. If you really want a more accurate answer you can start refining various figures but there's probably lots of factors unaccounted.

[turboplanner]

On 18/11/2021 at 12:40 PM, Old Koreelah said:

What does the methanol do? I presume it helps avoid icing and adds power;

 I don’t need any more power and I’m wary of any alcohol getting near all those rubber seals.

Methanol is Methanol; NEVER put it into your fuel system unless you are prepared to run half a litre of petrol through behind it after your system is drained. It eats a lot more than rubber; makes a nice meal out of an aluminium carby bowl, turning the result into a white powder which blocks airway and fuel galleries and if left long enough; a few months; completely block main jets and float valves.

 

Have a look at the MSDS sheet attached.

 

You could look at injecting methanol into the intake manifold after the carby becaise it would be going straight into the chamber at around 1300 < 1500 degrees and vaporising, but you're already on a winner with your system, and could look at cautiously upping the water in small increments; if I remember, you're after cooling. 

 

Cooling by methanol is practical in race engines because the engine will tolerate a level of richness that would drown it with petrol. You can certainly control your temperatures just by the main jets on methanol, and was able to eliminate first, cooling fans, and then air scoops and openings; engine cooling is totally by fuel. Have a look at a Top Fuelers dragster - no radiator. You could convert your aircraft engine to methanol easily, however two things are going against you (a) cost and infrastructure of the fuel, and (b) the nuisance factor of spening 20 minutes after you've used the engine to connect a petrol pot and run it through the carb.

WX00172.pdf

Edited November 20, 2021 by turboplanner

[Bruce Tuncks]

Thanks Aro, You may have found the mistake.

 

[facthunter]

Methanol itself is quite stable but is Hygroscopic  (seeks water). I have some drums I've had for 40 years and there's no clouding, sediment or rust at all. That's because they are well  sealed. You can have trouble with alloy carburetters and it's best to thoroughly drain them after use. Water is the issue as the same problem happens when the carbs have trumpets and no aircleaners and water gets in when it rains and you are on ordinary Petrol. The small passages corrode and the carb. is Junk.   Quite a few "PLASTIC bodied 4 barrell carbs were made at one time to get around this problem.  Nev

[Bruce Tuncks]

Going further, 1.33 cc/sec water turns into 1.75 litres of water vapor which dilutes the incoming 55 litres/sec of air but not by too much.

 

IF these calculations are correct, they indicate to me that the 80 cc/min water injection is about right.... significant cooling and not too much dilution.

[Old Koreelah]

During the week I installed a more powerful water injector system (a windscreen washer kit- thanks Cosmicray) and this morning I tried it out, first with the plane tethered to a post- in case the extra water puts out the fire.

 

With the output set to 200ml per minute, it’s spraying at least as much water into the engine as fuel- a 50/50 mix.

 

Previous test flights with c.80ml/min only cooled the CHTs a few degrees; this time the air intake temp probe (which cops the water spray) dropped almost ten degrees and the CHTs quickly cooled to an average of 130C! 

The pump only operates at full throttle, so as soon as I back off the power, the heads heat up considerably. 

 

[skippydiesel]

6 minutes ago, Old Koreelah said:

.................................................................................................

The pump only operates at full throttle, so as soon as I back off the power, the heads heat up considerably. 

 

What impact (if any) does, the seeming rapid,  heat cycling, have on engine service life?

[turboplanner]

6 minutes ago, Old Koreelah said:

During the week I installed a more powerful water injector system (a windscreen washer kit- thanks Cosmicray) and this morning I tried it out, first with the plane tethered to a post- in case the extra water puts out the fire.

 

With the output set to 200ml per minute, it’s spraying at least as much water into the engine as fuel- a 50/50 mix.

 

Previous test flights with c.80ml/min only cooled the CHTs a few degrees; this time the air intake temp probe (which cops the water spray) dropped almost ten degrees and the CHTs quickly cooled to an average of 130C! 

The pump only operates at full throttle, so as soon as I back off the power, the heads heat up considerably. 

 

A couple of things here; you are not measuring combustion chamber temp which will be around 1,000 to 1,500 deg C. That's only temporary, at peak combustion stroke, but I'm a bit nervous about sudden injections of a lot of cold water, and intermittantly and what that could do to the metallurgy. From my reading over the last ten years, most upper cylinder failures were not on WOT take off but at cruise rpm during the flight.

[facthunter]

Take off has to  be the most critical and stressed time of an engines life and often has a time limit at that power setting. Damage done then may result in an engine failure  an hour or so later. The Take off % wise is a small part of the total engine time. Nev

[Old Koreelah]

27 minutes ago, turboplanner said:

…I'm a bit nervous about sudden injections of a lot of cold water, and intermittantly and what that could do to the metallurgy. From my reading over the last ten years, most upper cylinder failures were not on WOT take off but at cruise rpm during the flight.

That has my attention. There is a time lag of about ten seconds between hitting full power and the CHTs starting to climb. I presume that’s how long it takes for the heat to travel from a few mm from the combustion chamber to the probes

 

Perhaps the ideal is to gradually ramp up cooling water and taper it off after backing of the power. How to do that without over complicating the setup? 

 

I mucked up my maths; the current water rate of 200ml/minute is about 50% of the amount of fuel it burns at WOT.

[Old Koreelah]

24 minutes ago, facthunter said:

The Take off % wise is a small part of the total engine time. Nev

And a good thing too; I only carry enough water for 6 minutes at full power-enough for three 1000’ climbs.

[facthunter]

When the water stops you are only facing the situation you would have had without water at that particular throttle setting. How good is it after a gliding approach you do a go around at full Power? These are small motors with individual  cylinders and heads and should take thermal shock better than a lot of others. Nev

[turboplanner]

1 hour ago, Old Koreelah said:

That has my attention. There is a time lag of about ten seconds between hitting full power and the CHTs starting to climb. I presume that’s how long it takes for the heat to travel from a few mm from the combustion chamber to the probes

 

Perhaps the ideal is to gradually ramp up cooling water and taper it off after backing of the power. How to do that without over complicating the setup? 

 

I mucked up my maths; the current water rate of 200ml/minute is about 50% of the amount of fuel it burns at WOT.

Those maths sound more benign. I've seen a few mixture ratios from people who sell water injection kits but can't remember where just now.

[facthunter]

The results seem adequate. I've put water in at a higher rate than that without any sign of putting the fire out.. Be interesting to see what effect it has on removing the carbon. Make sure no water is going into the carby . Water Methanol in a  RR Dart 532 series make s a lot of difference to the Power obtained.  Nev

[Old Koreelah]

Hope you are right, Nev.

I always gradually advance the throttle lever over about five seconds.

All my approaches are glides at idle and I make a habit of closing cowl flaps to about 1/4 when backing off in the circuit. Despite this, by the time I cross the keys the heads are down around 100C.

 

[Old Koreelah]

4 hours ago, facthunter said:

When the water stops you are only facing the situation you would have had without water at that particular throttle setting. How good is it after a gliding approach you do a go around at full Power? These are small motors with individual  cylinders and heads and should take thermal shock better than a lot of others. Nev

Hope you are right, Nev.

I always gradually advance the throttle lever over about five seconds.

All my approaches are glides at idle and I make a habit of closing cowl flaps to about 1/4 when backing off in the circuit. Despite this, by the time I cross the keys the heads are down around 100C.

2 hours ago, facthunter said:

Make sure no water is going into the carby..

That’s exactly where it goes Nev; remember that earlier in this discussion you suggested that. Since the water only pumps at full throttle, it should go straight thru to the combustuon chamber. I’ve mounted the reservior below the level of the spray nossle to prevent syphoning when the pump is not running.

[cosmicray]

I initially experimented with spraying water into the carby (AeroInjector) and got good CHT cooling with my Jabiru 3300. Now I have created a permanent installation injecting through a Snow nozzle after the AeroInjector and before the inlet plenum. The cooling result is slightly less effective but I didn't feel comfortable spraying water into the mouth of the AeroInjector. In an internal combustion engine, water injection does not increase power until the timing is adjusted to take advantage of the increased cooling headroom. More power equals more heat.

[facthunter]

OK the original idea was to try it out that way. (simpler)  Long term I would be more cautious about the idle system passages.

   . Cosmicray. More mass  equals more molecules bouncing around,  equals more pressure means more power. Advance may help but just use it as more safety margin. leaving it where it is. Jabiru retarded it as a part of the engine safety package and coupling it with the water actuation is likely to make things more prone to failure.

 OK, the slow throttle is good technique but sometimes you are compromising your situation IF extra power is critical quickly. A CV Carb is not too likely to hesitate.  The dashpot closes almost completely and that covers the slow operation and acceleration  well. 101 to 105 (counting) can be precious seconds There is not a lot of flywheel to oppose the revs rising quickly initially. Pistons come to rest twice per revolution anyhow and it's NOT a high RPM motor.

   No ones tried mixing some meth. Things that I've been involved had methanol mix. I don't know the %. It was supplied by the aircraft fuel companies direct.  There are some risks with everything you try. Leaving an inhibited motor unused we know is a bad idea.   Nev

[turboplanner]

36 minutes ago, facthunter said:

OK the original idea was to try it out that way. (simpler)  Long term I would be more cautious about the idle system passages.

   . Cosmicray. More mass  equals more molecules bouncing around,  equals more pressure means more power. Advance may help but just use it as more safety margin. leaving it where it is. Jabiru retarded it as a part of the engine safety package and coupling it with the water actuation is likely to make things more prone to failure.

 OK, the slow throttle is good technique but sometimes you are compromising your situation IF extra power is critical quickly. A CV Carb is not too likely to hesitate.  The dashpot closes almost completely and that covers the slow operation and acceleration  well. 101 to 105 (counting) can be precious seconds There is not a lot of flywheel to oppose the revs rising quickly initially. Pistons come to rest twice per revolution anyhow and it's NOT a high RPM motor.

   No ones tried mixing some meth. Things that I've been involved had methanol mix. I don't know the %. It was supplied by the aircraft fuel companies direct.  There are some risks with everything you try. Leaving an inhibited motor unused we know is a bad idea.   Nev

Methanol is not a good move unless you want to dedicate time after each flight (or day to remove it) Race Car operators have moved from draining the carb bowls the following day (because that wasn't quick enough to avoid damage) to connecting a portable petrol pot and running the engine on petrol after draining the bowls at the end of the race meeting.

[facthunter]

It IS an issue but where you only ever use it at full throttle and take off the  rest of the flight is on straight petrol which should make the problem much less. I still urge some caution. I have Methanol in original drums that is over 30 years old and no sign of corrosion in a normal drum. On the other hand I've had oil tanks for total loss systems rust out  the bottom even though oil was always in them. Nev

[Bruce Tuncks]

Thanks old K.

If the water injector setup is enabling you to keep the temps under 160 C  then that is just great.

[Old Koreelah]

Turb’s reservations got me thinking. I’ve spent lots of time installing cowl flaps to avoid shock cooling, but hadn’t considered the sudden cooling by water. Worse, my new water injector sprays almost four times as much water as the old one; after a few seconds on full throttle the CHTs all drop quickly.

Adjusting that rate is a tedious job. As I mentioned earlier, I have a disused oil injector in the rubber coupling downstream of the carby, so I could relocate my water injector to that location. That would make it safer and more accessible for fine adjustments.

 

It occurs to me that the ideal spray rate starts small and increases with revs;

Maybe link the throttle lever to a reostat to vary the power of the pump.

Or link the throttle to a constrictor valve

Why not have it controlled by the intake vacuum… That means a second carby! Not gonna happen.

 

 

[facthunter]

I think you are overthinking it. Keep things simple. You are not managing a 2500 HP motor.Nev