Rover piston melting point

[Ian Anderson]

I've been watching this thread wih interest

What about warer injection in the inlet airflow.
1) It cools the charged air via evaporation
2) It increases the charged air density
3) It supposedly reduces combustion temp.

Now how much of this is accurate and how much just pub talk I don't know

Ian

[mgbv8]

I found out the problem I was having on the old engine was too small a ring gap. I also know that the front 4 on my engines tend to lean out due to the carb config. The leaning out on the front 4 was causing high temps in the front 2 pistons. The rings were closing up and causing this hot spot which caused the ring lands to fail at the ring gap area time and time again.

I'm now going to install a second set of solenoids to serve just the front 4 with a richer mixture which should stop this problem for the time being.

This is a stop gap mind. When I rebuild this new engine I will gap the rings accordingly.

Its a bit of quandry though. I may not even suffer the same problem on the new 4.6 as it should gobble more gas than the old 3.5 before it develops the same fault.

I'm just hoping to get a whole season out of this one before I melt anything.

ian
water and methanol injection is supposed to work really well.

[kiwicar]

hi Ian
the big deal with water injection is suposed to be what it does in the combustion chamber as the mixture burns. As it is a liquid that takes no actual part in the combustion it absorbes alot of energy in the form of heat as it goes through the change from liquid to gas (water to steam). This is ability is referred to as latent heat capacity and is high for water. With the piston approaching TDC on the compression stroke the mixture is lit by the spark plug and the flame front moves off across the combustion chamber. As this happens the charge gets hot and expands rapidly, with the piston still moving up, and the products of combustion expanding rapidly, the pressure in the combustion chamber goes up. This raises the heat across the chamber and before you know it, you get combustion starting off all over the combustion chamber (fine if you burn diesel) not good for a petrol engine. This is not good because pretty soon the pressure and temp go up even further and you have detonation !
What the water does is, being mixed in with the charge, as the piston comes up and ignition starts, the water absorbs some of the the heat as it turnes to steam. This reduces the temperature of the flame front and slows the rate of expansion of the charge initially. More importantly if the charge does start to self ignite due to local hot spots the latent heat capacity of the water can be enough to supress this and delay it starting all over the combustion chamber.
The key thing is that the steam cannot start to rise in temperature and expand until it has absorbed the latent heat energy.The steam will expand as it's temperature rises to match that of the rest of the combustion products, but it is delayed long enough for the piston to pass TDC and the piston is moving down the cylinder and the combustion products can expand. That is my understanding of what is meant to be going on any way.
Mike

[Ian Anderson]

Mike

thanks for that

I had heard of it mainly on diesel engines and presumed it would also be good on the petrol variety.t
I also know they use it a lot on aircraft engines to add to the thrust required on take off. About 500l for a take off per engine if memory serves me right. (Based on 707 technology long haul) But then a different type of engine again!


Ian

[kiwicar]

yup in turbines it is the conversion of heat from the combustion of the fuel into the expansion of the steam that gives the extra thrust, it also allows the turbines to run cooler for a given fuel/air charge. The same is happening for a diesel internal combustion engine (heat is the big killer in a gas turbine, that is partly why they run better at high altitude where the air incomming is very cold). In a petrol engine the same should apply, however I believe the biggest benifit in a high revving petrol engine is from the delay in detonation and a lower peak cylinder pressure. An engine running with water injection is meant to be much kinder to pistons, con rods and cranks.
Mike

[mgbv8]

Great bit of info there Mike. Thanks.
I know a guy with a Turbo'd Rotary engine in a car that runs very quick (9 seconds) who uses water injection and he swears by it for his car.

[CastleMGBV8]

Perry,

I think some of the high output Subaru turbo engines run water injection as standard.

Kevin.

[stevieturbo]

Perry,

I think some of the high output Subaru turbo engines run water injection as standard.

Kevin.

No they dont.

I know of no factory car that runs WI as standard.

Some Subarus do have a water spray facility onto the intercooler core. But not internal water injection.

[CastleMGBV8]

My mistake, new there was water involved somewhere in the system though.

Kevin.

[mgbv8]

Yes!!
And some of the spray bar boys often slow racing down dont they Stevie?

Dripping all over the start line...