Engines can be damaged by operating at high power settings with too lean of a mixture. Valve, head, or cylinder damage will likely occur. I read or saw somewhere that they used a richer mixure on the very outer injectors to keep the nozzle cooler, but this video says they dumped the turbine exhaust on the inner wall of the nozzle to keep it cooler, either way it is a cool video. You are logged in as a guest. Forums Classifieds 54 Skins Language. Why does lean fuel make an engine run hot?
View previous thread :: View next thread. Message format Flat Threaded Nested. Mark in NEMO. Northeast Missouri. Something I've always wondered Engine gurus? Fuel has a quenching effect. A lean mix is a dry mix. Burns hotter. Nashville, IL. I'm not sure as to why, but I would guess has to do with air to fuel ratio.
The fuel acts as a coolant. I know on the pulling tractors, we run more fuel than needed to help cool. I had a truck set up for a while and you could watch the egt's drop as it started to overfuel.
A simple way, is just think of frying something dry in your stainless fry pan. It seems to work better with a bit of oil Think of your blowtorch how do you get it to burn hot: oxygen.
Matt NMO. Keep turning the oxygen up and the fire goes out eventually meaning leaner is cooler. If you want to make max power and not melt things you have to add water. Mercedes is supposedly working on a six cycle diesel which uses water alone as fuel on the fifth cycle. I'd just like to figure out how to rig an exhaust heated water injection system which would fire a metered amount into the jugs with the fuel air mix The only real question is can that lil six handle it.
One thing to remember is that the mixture isn't homogeneous, so even at stoich there are lean and rich zones in the burning charge - which means that in order to get every BTU out of the fuel you have to run leaner than stoich.
Actually much for the same reason that most drifters run their engines extra rich, especially if they are running a big turbo. Just like chilehed said, most modern cars are actually ran richer at high loads to cool it down, hence if you run the engine lean, it runs hotter :lol:.
It's going to be powering their new super car too, the one with auto cambering wheels and stuff This thread has focused on the ability of excess fuel to carry away heat. However, I found an alternative explanation for why lean engines run hot that sounds very convincing to me:. Peak flame temperatures don't cause any damage to pistons, but it takes far lower mean cycle temperatures to damage them, usually first from lubrication failure before outright melting. However, I admit that I don't fully understand why slow combustion would raise the mean cycle temperature.
It's not like the combustion products stop being hot once combustion is finished! My best guess is that if combustion is rapid before the piston has moved far then the expansion ratio is maximized and the gases can most quickly expand and cool down. You can post now and register later. If you have an account, sign in now to post with your account.
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Share More sharing options Followers 0. Reply to this topic Start new topic. Prev 1 2 3 Next Page 1 of 3. This and some other effects makes the final flame temperature lower. Based on some extended conversation on the question, let's put this all back into the context of an engine. For a direct-injection gas engine, the air is sucked into the cylinder, the piston compresses it, and then fuel is sprayed into the cylinder.
A spark plug then triggers a spark in the chamber. This deposition of electrons gets the fuel-air mixture molecules all excited -- it actually ionizes the air strips off electrons from the molecules and this all adds a bunch of energy to the molecules. This energy is the initial energy required to start the combustion.
For a fuel-lean condition, I said it takes more energy to start the reaction and I phrased it in terms of a higher ignition temperature. The ignition temperature comes from that spark plug for a cold engine -- hot engines will also contribute heat from the cylinders themselves. For normal operating conditions, spark plugs provide more than enough energy to ignite.
As the operating condition gets leaner, the spark plug provides the same amount of energy -- but it is still enough energy to ignite. Eventually, for lean enough conditions, it won't be enough energy. This is a lean misfire. Diesel engines work differently. For sake of argument, let's stick with a direct injection again.
The cylinder fills with air, the piston compresses it, and the fuel is injected. There is no spark to initiate the reaction though. Diesel engines rely solely on creating high enough pressures to ignite the mixture. High pressure means high density and that means more collisions to spread the energy around molecules don't need to go as far to hit one another. At any rate, the same ideas apply. In lean conditions, it would require a higher pressure to ignite. At ideal conditions, the engine compresses more than is exactly required, so when it runs fuel-lean, it still has enough compression to ignite.
If you go so lean that the compression isn't high enough anymore, you will again get a lean misfire. Glow plugs can help all this by heating the cylinders and helping to add heat to the mixture and get the reactions going. In either engine, once they have been running for awhile, the cylinder walls heat up and it requires less input from sparks or from compression to make the reaction occur.
But for cold engines, it needs that initial energy deposition to get the reactions moving along. Many ECU's are set to burn fuel-rich when the engine is just starting because it is easier to ignite; as they heat up, the mixture becomes more lean and reduces emissions and fuel consumption. You may be familiar with manual chokes on things like lawn mowers -- the choke is what changes the fuel-air mixture and to get the motor started, you have to set the choke to be fuel-rich.
The conversation in chat is bookmarked here. First lets make sure of our definition. In my reading there are two effects. First, the fuel is an atomized liquid which has a cooling effect on the combustion chamber. So less fuel, less cooling effect. Second, flames burn faster and hotter in the presence of more oxygen.
More air relative to fuel than usual, means more oxygen than usual. So the flame burns hotter and faster than it should. Both are going to raise the temperature of the combustion chamber. If you have ever seen an oxy-acetylene torch being used, you will have noticed that before the oxygen is turned on, the torch has a bright yellow flame. This is the fuel burning in a less than ideal amount of oxygen.
The flame is relatively cool and it produces a lot of soot. In an engine, the fuel wants to burn efficiently, but not too hot that it starts to melt the pistons, or maybe even violently explode, which will also cause damage.
From Wikipedia - A stoichiometric mixture unfortunately burns very hot and can damage engine components if the engine is placed under high load at this fuel—air mixture. Due to the high temperatures at this mixture, detonation of the fuel—air mix shortly after maximum cylinder pressure is possible under high load referred to as knocking or pinging.
Detonation can cause serious engine damage as the uncontrolled burning of the fuel air mix can create very high pressures in the cylinder. As a consequence, stoichiometric mixtures are only used under light load conditions.
For acceleration and high load conditions, a richer mixture lower air—fuel ratio is used to produce cooler combustion products and thereby prevent detonation and overheating of the cylinder head. The temperature engine rises because the ignition of the fuel is slower. It takes longer for the fuel to burn because there is less of it. The fuel itself has the same amount of BTUs available by burning it whether you use extra oxygen or not.
When you blow on the coals in your fire, they get hotter but burn faster. They release the same amount of heat, but in a much shorter period of time.
Imagine your cylinder as a cabin in the winter. If you took a log and burned it in one minute, the items near the stove where that log was burning would heat up significantly and maybe melt, but most of the heat would go out through the chimney. One is that an engine running lean—meaning too much air is going into the cylinders—tend to run hot. Jason Fenske of Engineering Explained busts that myth in this video. The ideal ratio of gasoline to air for combustion is A lean mixture contains more air than that, more than can actually be used in combustion.
The opposite of a lean ratio is a rich ratio, which has less than Temperatures actually tend to peak with that ideal ratio, decreasing both when an engine is running lean and when it's running rich, Fenske said. High temperatures also correspond to high levels of nitrogen-oxide NOx emissions, one of the main pollutants created by internal-combustion engines, Fenkse noted. The chemical reaction that creates NOx occurs at high temperatures, he said.
Why does running lean or rich cause temperatures to drop? Because of the leftovers.
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