Patrol 4x4 - Nissan Patrol Forum banner

1001 - 1020 of 1058 Posts

·
Registered
Nissan
Joined
·
64 Posts
Sorry mate, do you mean Hobbs switch to control pre turbo?
Hahaha yeah sorry I haven't had much do do with these switches I just keep thinking of anti grenade kits with drawes and all the other things. So am I on the right track? And where would be somewhere good to get a Hobbs switch from?
 

·
Administrator
GUII ZD30DI Wgn
Joined
·
43,842 Posts
Hahaha yeah sorry I haven't had much do do with these switches I just keep thinking of anti grenade kits with drawes and all the other things. So am I on the right track? And where would be somewhere good to get a Hobbs switch from?

You could start here, I put up a pic of the various Hobbs switches earlier, I have a NC 14-24psi, go through that listing and choose what you need then you can find it on ebay.
 

·
Administrator
GUII ZD30DI Wgn
Joined
·
43,842 Posts

·
Administrator
GUII ZD30DI Wgn
Joined
·
43,842 Posts
Was going through some old paperwork and found something from a discussion on DO's own forum about pre turbo in general, many against and with some strange opinions on what happens and density. Good read even though it's about a Subi, the calculations are interesting. With thanks to Devils Own, here are Thermodynamic calculations on water absorption of heat during compression at the turbo impeller. Would be interested in @OldMav view, especially with the Turbo Tech thread making headway.




The calculation is in 4 parts and relates to a WRX STI 2.5 L turbo car.

Part 1 Assumptions and definitions
At 15-16 psi the engine is consuming ~250-275 g air/sec
Temperature of compression at 60% turbo efficiency, produces ~100 degrees C change at 7000 RPM
Heat of evaporation 540 calories/ gram of water
1 calorie = 1 degree C/ gram/sec at one atmosphere
1 calorie = 4.184 joules
Specific heat of nitrogen gas 0.25 calories/degree C (air is mostly nitrogen)

Part 2 Heat change under compression and amount of water to restore starting temperature
For 1 degree change in water temp we get 1 calorie*grams/sec.
For 100 C change (increase) of air (nitrogen) of 1 gram = 25 calories to heat 1g of air 1 degree C
540 calories/gram of water evaporated, heat of evaporation
Too cool 250 g air / sec heated 100 C costs 250*25 or 6250 calories / sec
6250 calories/ 540 calories/g water is 11.6 g water / sec = 11.6 ml water/ sec or 695 ml of water / min
Thus, 695 ml/min of water brings the compressor to isothermal compression with 100 C change in temp
during compression.

Part 3 Engine's consumption of air at 7000 RPM in a 2.5L engine
For a 2.5 L engine at one atmosphere and 7000 RPM, that's 3500 cylinder fillings per min,
or 2.5L * 3500, or 8750 L / min * 1000 ml/L =
8.8 million ml of air / min
At 15 psi of boost the amount of air is double or 17.5 million ml / min
695 ml/min cools 17.5 million ml/min air 100C or
0.004% (by volume) water to air ratio = isothermal compression with 100C temperature change

Part 4 pre-turbo injection effects with on the set up
100% stated "efficiency" of a turbo compressor is not isothermal, but adiabatic compression.
With and a 2gph jet I can inject about 125 ml / min, that is about 18% of 695 ml / min.
The turbo is operating at ~60% adiabatic efficiency at 7000 RPM, the 695 ml/sec water to brings it
to isothermal compression which corresponds to about to 118% efficiency at a pressure ratio of 2,
a difference of 58%.
18% (125 ml/min) of 58% is 10.5%
60% efficiency of turbo + 10.5% cooling from water = 70.5% efficiency of compression adiabatic.
250 ml / min water injection gives twice that or 81% compressor efficiency.
So with just 250 ml/min pre-turbo water injection, compressor efficiency is near 80% at redline, quite a feat!

It's like having a 20% larger turbo!
I don't know the actual change in temperature during compression at 7000 RPM on an '04 Subaru STI with the stock turbo. 100C is a reasonable guess, but it could be as high as 150C if the compressor efficiency is lower than the predicted 60%.
Thus, these numbers are only a rough estimate. While isothermal compression would be nice to achieve, I think one should be happy with just extending the efficiency of the turbo beyond it's normal bounds, and make up for the adiabatic heat by injecting more water/meth after the intercooler. Under this scenario maximum total water injection is 15% of fuel mass, very reasonable.
 

·
SUI GENERIS UTE
GQ Ute 1990 Silvertop
Joined
·
5,842 Posts
Very interesting.

I did some math like that a few years ago. He must be a physicist as not too many would know about adiabatic compression when efficiency points go above 100% which is sort of impossible because the comp map is adiabatic compression 100% is absolute.

But what i did was use absolutes and converted back from isothermal compression into the map with a constant density ratio to adjust lbs/min each pr point in displacement. So in simple terms i just used or built another compressor map which worked out to be for a 4.2 litre diesel going from a 67mm comp wheel to a 76mm comp wheel for most of the 4.2's rpm range.

In the real world you can calc back from your dyno chart if you measure inlet and outlet temps against the loss imposed in drive required from the turbine with guess work on flow with temp in and out to get a efficiency point at max torque. Due to losses from the extra drive required on the turbine side to compress the heavier comp mixture we end up with a bit better than 18% more density on our diesel at peak torque obviously with enough water, this is very dependent on how good your turbine is to drive the comp wheel to compress the same heavier volume. On my KKK after 650 to 700cc/min there is diminishing returns as my KKK turbine cannot drive enough to compress this heavier air mixture at peak torque rpm.

This guy was doing this for 7000 rpm where drive on a petrol is probably not a issue and he has not factored in this part of the equation either so his values are much higher than i calculated and more than what reality is in the real world, especially when you are using 60% efficiency choke values. i was using 74% at peak torque with drive losses.

All in all it is a good exercise and goes to show pre turbi injection is like having the next size up turbo on your car especially if you are looking for bigger power torque numbers to do faster quarter miles.

For me i use it to increase boost/density response and transitions/driveability it can cover a multitude of turbo matching sins thats for sure. For a diesel it does make the comp map fit a lot better to a diesel with not having to worry about pumping heat instead of volume when you start hitting those 60% efficiency point. It makes the comp map wider with the efficency islands wider and taller and a extra few % added is all it does if you are looking at comp maps to see the differences. It doesn't do the big % increased values like he is suggesting, it could and would if the turbine could magically flow more with less emp when water is added on the comp side.. The two wheels are joined together, what one does the other has to compensate for the change its not all up in the good nice to have direction in the real world.

Obviously this is about pre injection and a nice bonus as anybody who has gone down the pre turbo injection path will tell you with enthusiasm abound. But to back all this up there isn't really a huge increase like the poster suggests with just pre injection. After injection puts the icing on the cake to complement the density gained especially if you inject close to quench point at all load rpm points.

As you know and is worth doing for free water, but it does require big volumes to get to the ideal including big tanks which poses a problem in a already space short wagon..
 

·
Administrator
GUII ZD30DI Wgn
Joined
·
43,842 Posts
any thoughts on having tanks made up behind the bullbar or do you think front weight is not ideal
Yes you can do it but your mounting would need to be very solid, remember 1Kg per Litre, also it is best to have the pump close to the tank and below it, so you need to take all those things into consideration. When I did mine I looked at this option but decided against it.
 

·
Registered
Joined
·
5,283 Posts
Ideally the pump should be below it.
Mine isn’t and is fine, my tank is under the passenger between chassis and body, pump is in the engine bay near the over flow bottle.
I’ve tested it while driving having it point out of the bonnet and there is no delay.
Don’t stress to much.
 

·
Registered
Joined
·
224 Posts
Had a good giggle watching this video. Pretty much just a garden sprinkler hosing water straight into the compressor. I read some of his comments later on saying he was getting lots of water pooling further along the intake pipework. I think it's safe to safe any attempts I make going down this path will be slightly better than this LOL!

https://www.youtube.com/watch?v=cj_XV3g9W3o
 

·
Registered
Joined
·
224 Posts
Managed to do some more testing today and went for my first drive with pre-turbo switched on. Can actually feel it kick in while driving compared to just the manifold injection. I wouldn't say it's a massive difference but it's definitely noticable, I've only run the small nozzles so far so more yet to come.

 

·
Registered
Joined
·
224 Posts
Well my fun didn't last long lol. Blew the ass out of my hobbs switch which activates my pre-turbo nozzle. Accidently ordered the wrong part and didn't realise, burst pressure was only rated to 550psi, the diaphragm didn't stand a chance copping 1400psi :LOL: Surprised it actually lasted as long as it did. Sourcing correct parts today so hopefully back to more testing this weekend.

Found data sheet for the high pressure rated pressure switch if anyone's interested.
 

·
Registered
nissan
Joined
·
3,928 Posts
I'm confused, where and how are you generating 1400psi that is getting sensed to start your injection??
 

·
Registered
Joined
·
224 Posts
I'm confused, where and how are you generating 1400psi that is getting sensed to start your injection??
I'm running a Pumptec 113C positive displacement high pressure pump. It's only rated at a max continuous 1200psi but In my testing I've been well over 2000psi and she's still going strong lol.

Screenshot_20190925-180728.png
 

·
Administrator
GUII ZD30DI Wgn
Joined
·
43,842 Posts
I'm running a Pumptec 113C positive displacement high pressure pump. It's only rated at a max continuous 1200psi but In my testing I've been well over 2000psi and she's still going strong lol.

View attachment 513703
Have you checked the various flow rate between various injection pressures on a fixed nozzle? would be interested, even with my only 250psi max pump I had to drop down to around 210psi as flow rate increased and went through tank to quickly.
 

·
Registered
Joined
·
224 Posts
Haven't touched it since I blew the pressure switch. My new one rocked up yesterday but instead of the 1/4" bsp tapered like the previous it's a 1/4" straight thread process fitting so I need to go out and grab some copper washers for it to seal. There's always something slowing down my progress lol.

I do plan on testing flow rates at various pressure though when I have time. In the little testing I did do, maybe 1hr total driving time I've already had to refill my 50L tank once so I'm pretty sure I won't be stay at 1200psi for much longer either lol. Although I was testing and was on boost pretty much constantly so doesn't really replicate normal driving.
 
1001 - 1020 of 1058 Posts
Top