Recenty I had the opportunity to get the old 2-burner Coleman gasoline stove out. You know how the kind you pump to pressurize? Well, the fuel line runs over the burner so that the gas is vaporized prior to burning. Before it heats up sufficiently, you turn a valve UP (to mix in air); after its good and hot DOWN to run on straight gasoline.
Always burns with a clean, blue flame; generally takes soot OFF pots and pans.
I also remeber hearing here that the big pollution issue is undissolved aerosol gasoline; IC engines that run on propane or natural gas have virtually no pollution.
Putting 1 and 1 together, why not pre-vaporize the gasoline by passing it inside the exhaust manifold? You’d (seemingly) get the pollutions benefits of CNG without conversion and fuelling issues? (I APOLOGIZE that this site does not allow me to input paragraph breaks ?!?)
You’d essentially be creating your own vapor lock and possibly an emissions and safety nightmare: Manufacturers go to great pains to avoid routing fuel lines near things that get hot.
There’s a big difference between running a stove burner in the open air and repeatedly detonating a gasoline charge in a cylinder too. Your stove burner also may look like it’s burning nice and clean, but in actuality you have no idea how efficient it’s running and what it’s putting out into the atmosphere. I’m willing to bet it’s not as great as it looks, just because it’s burning blue.
One part of what you suggest does have some merit though–manufacturers are beginning to use exhaust heat to warm up coolant. This enables the engine to much more quickly reach the ‘sweet spot’ of normal operating temperature so emissions and driveability are improved overall.
You raise an interesting question, but the reason LNG and propane burn more cleanly isn’t because the fuel is better vaporized, it’s because the fuel has a lower carbon content. The combustion process is the same, but the difference in the fuel creates a different result.
Well, not quite the same combustion process. The spray from fuel injectors creates millions of tiny gas droplets that mix with intake air but can’t totally vaporize in the short time before the spark, so the burning takes place in the droplet surface and burns inward, sort of like a tiny globe on fire. This is not an ideal combustion process because the fuel and air are not perfectly mixed. I don’t remember all the ramifications of the burning droplet type of combustion, but my recollection is that it’s not as “good” in some measure as a fully premixed (vaporized) fuel.
Propane and CNG are already vaporized, so there are no liquid droplets to burn in a less-than-ideal way.
True, but carbs are really not very good at vaporizing fuel. Especially at low engine speeds, where the lateral wall pressure is relatively high (vacuum low) and the pressure difference between the float bowl side of the orifice and the carb throat side of the orifice is small.
It’s like a Windex spray bottle. Squeeze the sprayer softly and slowly and the Windex comes out in large droplets and drips down the bottle. Squeeze it hard, creating high pressure differential, and a nice fine spray comes out. Injectors use high pressure to vaporize the fuel, generally 40psi or higher. Carbs use very low pressure. They rely primarily on the vacuum, the low lateral wall pressure.
Isn’t one of the benefits of direct injection that it cools the air during compression, allowing higher compression ratios (and therefore greater efficiency)? Preheating the gas would eliminate that benefit.
The intake valve isn’t open during the compression cycle, so there’s no way direct injection can affect the gas (air+fuel) volume in the chamber for more compression. Chilling the contained gasses would serve to reduce pressures rather than raise them.
You’re probably thinking of the intake cycle, and you may be right, but you can’t change the contained volume once the intake valve closes. The compression pressures are going to be a result of that captured volume, the compression ratio and the rise in temperature generated by compression (and some amount absorbed from the cylinders).
Port injection, however, would also cool the gasses as they pass into the chamber past the intake valve, so I don’t know if direct injection has any benefit in that regard. As I understand direct injection, its primary benefit is that the fuel spray avoids the turbulence of the intake valve & port, thus providing a cleaner vapor in the cylinder.
But I could be wrong. It wouldn’t be the first time. I think it’s a very interesting question. I’ve just never thought about it before.
Direct injection doesn’t affect the compression, it allows using a higher compression ratio. Mazda’s ‘Skyactiv’ technology uses direct injection and a 14:1 compression ratio with regular gas.
It doesn’t affect the compression ratio, which is a purely mechanical calculation, but if your earlier post is correct it affects the chamber temperatures and thus the cylinder pressures. That may be why it allows 14:1 ratios with regular gas. The actual pressure built up after the gasses are compressed with the incoming fuel having cooled the air as it enters the chamber may actually be no higher than it would be with port injection. The denser air would seem able to allow more intake volume, but it would be offset by the air molecules being less active. Thus, perhaps the chamber gasses don’t rise high enough to self ignite.
You’ve presented an interesting technical question. I’d be interesting in hearing input from the others here who are versed in these things. These are the type of threads I enjoy the most.
From what I’ve read charge stratification plays a part in allowing the high compression of ‘Skyactiv’ etc.
The fuel injection is timed so the air fuel ratio is relatively rich in vicinity of the spark plug when it fires, but lean in the far reaches of the chamber where detonation tends to occur.
I’m not qualified to venture an answer but that Coleman fuel scares the heck out of me. We were camping and the fire was having some trouble getting started so I took a half a styrofoam cup of Coleman fuel and threw it on the fire. The resulting fire ball singed the hair on my arms UNDER my jacket. Never do that again and if the fuel line ran over the burner, I sure wouldn’t want to be using that stove, myself.
That’s where they’re going, I think it’s Mazda that has a gas engine that runs like a diesel (no spark needed) under development. One reason that diesels are losing their mpg edge over gas engines, especially when price is included.
I have a Coleman gasoline stove outside on my garden bench I use to heat sterilize my indoor potting soil. I put the soil in a big pot and heat it to 180 deg F.
I don’t use the Coleman camp stove fluid. I use plain unleaded 87 octane gasoline I buy at the gas station. Not recommending this, not even sure if it is safe, but it has worked fine for me for years. I can tell no difference w/how the stove works between 87 octane gasoline and Coleman camp stove fluid.
One thing that has always puzzled me is that input tube to the burner. How it runs across the flame. Inside that tube there’s a thin, stiff wire called the “generator”. It’s not a straight wire, it zig zags back and forth. If that wire is removed, the stove won’t work. I’ve always wondered what is the purpose for that wire? I thought it was sort of like a catalytic converter, platinum coated maybe, so to catalyze some of the gasoline going through that tube, making it into easy to burn hydrogen gas. But someone told me that’s not how it works.