Thursday, October 30, 2008

How do internal combustion engines work?

I still need to post about the pros and cons of nuclear energy. However, this post is my explanation for why I've not posted anything for a week.

How do internal combustion engines work? This is not a question posed to me by my son, my friends, or anyone else. I'll explain the purpose of posing this at the end.

An internal combustion engine like what you have in your vehicle works by mixing fuel (gasoline, diesel, etc.) with air, compressing it to very high pressures, (or compressing the fuel to high pressures and then mixing with air in the case of diesel), and then causing the mixture to explode or at least expand quickly, usually via some sort of spark (gasoline, etc.) or other high temperature device (glow plug: diesel). This explosion pushes a piston to move down through the combustion cylinder. That moving piston turns something called a crank-shaft. This crank-shaft is connected to some sort of transmission. That transmission transmits (duh!) the rotational energy from the engine into rotational energy in the wheels via a drive train (which includes a bunch of stuff). There's a flywheel attached to the crank-shaft, which causes the crank-shaft to want to continue turning, even after the piston has reached its lowest point. The crank-shaft is designed such that at the piston's lowest point, it will push the piston back up through the cylinder, starting the internal combustion process anew. This happens over and over and over, causing two to four thousand revolutions of the crank-shaft per minute.

All of these metal parts moving against each other cause tremendous amounts of heat to be generated. The exploding fuel mixture transfers a lot of the waste heat to the engine components. So, there's a system for lubricating and one for cooling an internal combustion engine.

First, the moving parts are immersed in a low viscosity fluid that resists degradation at high temperatures. This is the engine oil. Engine oil is designed as a lubricant that can be heated to high temperatures without changing its properties very much. This lubricant has one main job: to keep the hot metal parts moving smoothly against each other.

The second part to keeping the engine working is the cooling system. There are two parts to this cooling system. First, the engine block is cast (usually in aluminum, steel, or sometimes ceramic) with a network of piping between the outer wall and the cylinders through which a cooling fluid flows. Secondly, a pump pushes that fluid through the block and into a radiator. The radiator has many small pipes which the fluid moves through. This gives the fluid a high surface area, allowing it to quickly cool as relatively cold air passes through the radiator. This works via a mechanism called forced convection (the name "radiator" is a misnomer). That cooled fluid is then pumped back into the engine block and is heated as it moves through the block back to the radiator. The coolant moves around and around, transporting heat from the engine and losing that heat to the surrounding air via the radiator. This effectively and efficiently keeps the engine at a reliable temperature so all of those moving parts can work well.

Here's the thing. The correct, reliable operation of the engine relies on efficient, well-calibrated cooling. That cooling requires coolant. When your radiator develops a hole through which the coolant can escape, the engine can no longer be cooled. When that occurs, a number of nasty things happen:

1) The engine and all of its parts heat up more than they're supposed to.
2) The oil, which is specially formulated to work under specific conditions is no longer working under those conditions, so it starts to degrade.
3) If the oil degrades significantly, it no longer lubricates the moving metal parts, allowing them to scrape against each other.
4) If the oil degrades significantly, it may vaporize, greatly increasing the pressure inside the engine. That pressure increase can be so great that it blows out the gaskets (seals) in the engine block. This is what is meant when you hear someone say they "blew out a head gasket."
5) If the pressure and temperature is a bit higher, the head (the part that the spark plugs and valves and some other components connect to, just above the pistons) can be warped due to the quickly changing size (materials change size when they change temperature) being mitigated in some places by bolts.
6) If the pressure is really high, it can crack the engine block.

I don't know how bad it is yet, but I almost certainly blew out the head gasket on my brand new 11000 mile, 2007 Tacoma. I may have cracked the block, and being the pessimist that I am, I suspect that is the case. Even if I didn't crack the block, the pistons may have scored the cylinders, in which case I might as well have cracked the block (the cylinders in this engine are specially lined and cannot be repaired once they're scored).

Toyota's MSRP for a brand new engine is $15,000. A rebuilt engine runs around $3-4k. If I only blew out the head gasket or warped the head, I can repair it myself for the cost of parts and several weeks to months of working on it in the evenings. If the block is cracked, I need a "new" engine. If the cylinders are scored, I need a "new" engine.

If I need a new engine: I'm toying with the idea of replacing the V6 with an 8-cylinder diesel engine modified to run on biodiesel, veggie oil, or other renewable fuels. But, I need to address some other issues before I can even seriously consider going that route (such as how certain things like stability control and other safety issues are specifically handled and whether they require the gasoline engine to operate correctly). There wouldn't be much difference in cost between a "new" gasoline engine and a "new" diesel engine.

Unfortunately, the truck is sitting in the street by our house because it completely stopped running just as I got home. November 1 is "snow plow" day, meaning we can no longer park on the street.

I cannot/will not start taking apart the engine to assess the damage in the street. I ordered a new radiator from Toyota on Tuesday, but when I went to pick it up today, I discovered they had ordered the one for a manual transmission. The automatic transmission in my truck relies on the radiator to help keep IT at the correct operating temperature. That's another story.

Anyway, I can't move the truck right now because I can't start it without a radiator, which I won't get until Monday. I can't assess the damage because it's not in my garage, and I can't even see how much oil is/was in the cooling system because the hose doesn't reach from the house to the truck (I just bought a new hose this evening while I was out getting the radiator that isn't the radiator), so I can't flush out what's currently in the block to see how bad the damage is.

I HAVE to move the truck before Saturday evening. I happen to have an anchor bolt built into the floor of my garage. I do not know how much stress it can handle, but it's pretty beefy. I plan on attaching one end of a come-a-long to the anchor and the other end to the truck and pulling it up the steep driveway, into the garage. The house happens to be at the top of a hill with a straight shot down the street to a rather cross street. Perhaps you'll see me on the 9 O'clock news this weekend. Don't worry, I'll be careful.

So, I've been rather bummed and not too excited about writing about nuclear energy. My apologies. I'll get back to it this weekend or early next week.

5 comments:

Jennifer said...

Wow, I totally forgive you for not getting to the post. I hope it all works out for you smoothly.

But being the smartypants you are, how did you manage to wreak such destruction upon your new Tacoma in the first place? And why isn't Toyota covering this under warranty?

If I were in Flag I would lend my gigantic muscles to pushing your car into your driveway. Let us know how it goes!

Grumpator said...

It is bad enough that you fried your engine, but the added bit about having a deadline to get your truck off the street must be incredibly frustrating! Good luck, and I hope the damage isn't as bad as you fear.

I am Moses. said...

So, I may know how engines, or whatever work, but that doesn't mean I'm not impatient and frustrated...

It turns out that I'd forgotten a very important thing about engines. They are most efficient at specific temperatures. So, the thermostat on an engine doesn't open to allow coolant to flow until the truck has reached a specific temperature. Because of this, I could start up the truck and put it in the garage without damage...after I had rerouted the transmission coolant so that it didn't spill all over the ground.

I am Moses. said...

A comment on the above comment....

1) I was impatient to get the truck home after cutting wood with my dad all day. I had Garion with me and didn't want to spend the rest of the evening waiting for a tow truck to get my truck and the trailer full of wood. As far as I can tell, a stick poked a hole in the radiator while I was driving over some thinning fields to get to/from good cuts.

Runbob said...

Hi Mo, a minor quibble with your Engine Destroying Cookbook - I don't *think* you can get boiling oil to blow a head gasket - overpressure in the oiling system just sends oil out the dipstick or crankcase breather. I think the blown gasket comes from the warped crankcase/head geometry as everything heats out of spec and gives combustion gases in the cylinders a non-traditional method of escape. Anyway, hope your truck is OK. My advice: whatever happened, DON'T take it apart this winter. Wait 'til spring!