I know more heat inside the combustion chamber makes more power, I always thought its because the hotter the burn the more energy it gives off/burns better, what is exactly the reason as to a hotter flame/burn inside the combustion chamber making more power?

Just incase someone ever tried to ask me why I don't want to bullcrap around, thanx.

 

o.k. you want to keep heat in the chamber because the combustion produces heat and the more you let escape the more power you lose, the more you keep in the chamber the more power you make, and the less you heat up the rest of the engine.

Bret

 

From what I can remember, the work done on a piston during the combustion process is equal to the integral of the pressure (in the cylinder) times the change in volume (piston moving down the cylinder). If there is excessive heat loss from the chamber then the pressure in the cylinder would not be as great, resulting in less work done on the piston, which in turn means less power. It's really more complex than that, but that's the short answer I think. Anyone else?

 

To quote an old mentor of mine: Heat and pressure are 2 sides of the same coin.

In a confined space more of one means more of the other.

 

To add to his question...... if you have 2 identical motors one iron headed and one aluminum headed.... will the iron headed motor make more power???

Ray
My guess it yes

 

Yes, all else being equal (timing, lack of detonation, ambient air conditions, etc).

BUT, it won't be that big a difference in power, and the weight savings off the car w/ aluminum heads over iron will more than make up for the power you would gain. It would depend also on coolant temperatures you were running at. The hotter the coolant, the more power but only if you can keep it from heating up the incoming air charge. Hotter coolant equals lower delta-T (temp. differential) which means less heat conducted out of the cylinder. Again, minimal to negligable in the real world though. We might be talking about 1-1.5% total power output here.

 

I understand more heat more power, but then why are some people using a 160 stat.

 

blackdog-
thats not the COMBUSTION temp, but the cylinder head and possible intake charge temp

 

The hotter any given amount of a gas, the more space it will occupy. I can't remember if this is Boyle's law or Charles' law, but it's one of them laws. If you keep the heat INSIDE the cylinder (the a/f charge), without letting it transfer into the walls and head, it will stay in the gases and keep them expanding (or they'll expand further than if much of the heat is lost to other parts). More heat=more cylinder pressure=more force being exerted on the piston. This is a little generic, but it works.

 

You are making me think back to when I was an undergrad, approximately 35 years ago! But as I recall, Charle's law did indeed relate the temperature and volume of a gas. The volume and temperature are directly proportional. So, more heat = more volume = more pressure = more rapid expansion of the combustion gasses = more torque.

That's one of the reasons heat rejecting ceramic coatings are useful: they keep heat in the combustion chamber and thus make more power.

Rich Krause

 

Speaking of caramics, I spoke with a Ceramics and Materials Engineer (who is one of the campus faculty) last semester and he took me into the lab/shop where they make the coatings and bake them onto parts (gas turbine blades in this case). The ceramic paste is the coolest stuff in the world. They put some in a pan and told me to punch it, so I did. It was hard as a rock! And none of it got on my fist. But if you just shake the pan or slowly run your fingers through it, it's like JELLO pudding (sticks to everything). Cool stuff.

He then proceded to TRY to explain to a feeble mind such as myself as to how this stuff works, but it went in one hear and out of the other (talking about molecular bonds, heat capacities, crystal lattice structures that have super-strong ionic bonds, etc....I don't remember much). But he did get something across- ceramics are one of the toughest compounds known to man.

He's the reason I'm getting my 383's internals coated.

 

My God!! 35 years ago..... you're almost as old as I am....... .

 

Rich Krause

 

You kids!

My undergrad started in '61.

 

Depends on the end-goal of that particular engine development program. Engine performance is not the only parameter an engineer is faced with when designing a powerplant. Although that would be nice. Just food for thought.

Take care