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Old 27-03-2016, 02:05 PM
parmas parmas is offline
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Default Re: Superoxygenated Water/Methanol Injection

NITROMETHANE Internal Combustion tips and tuning

Eventually, Edelbrock settled on a 20 percent nitro/80 percent methanol mix that added 40 hp.

According to Gene Adams, if you consider high-octane racing gasoline as the baseline fuel, replacing it with methanol-the best alcohol fuel-is worth a 5-to-10-percent power gain. But 80-to-90-percent nitro is worth two to three times the power of the alky

What's the secret? Nitromethane carries its own oxygen, so it needs much less atmospheric oxygen to burn. The theoretical ideal or stoichiometric air/fuel ratio for gasoline is 14.7:1. That means, 14.7 pounds of air are needed to burn 1 pound of gas. Methanol, which also carries oxygen, has a stoichiometric ratio of 6.45:1. But with 100 percent nitro, the ratio is 1.7:1! Because the displacement of an engine cylinder is fixed, this means-assuming 100 percent volumetric efficiency (VE)-8.7 times more nitromethane than gasoline can be burned during one combustion cycle.

On paper, gasoline has about four times more heating value than nitromethane: at least 19,000 Btu/lb for gas compared with just 4,850 Btu/lb for nitro. But that doesn't take into account the fuel's specific energy (SE) value, which is derived by dividing the heat value by the air/fuel ratio (Btu/lb ÷ A/F), telling us how much heat energy is delivered per pound of air into the motor. At stoichiometric air/fuel ratios, the nitro's SE value is around 2.2 times greater than gasoline!

Racing nitro motors run far richer than the theoretical 1.7:1 ratio, and Adams says it's possible to dump nitro at ratios approaching 0.5:1. "At 80 percent nitro and above, the optimum air fuel/ratio no longer exists and the power output becomes well related to the actual amount of fuel fed into the engine by weight," adds Ray Hall Turbo. At 0.5:1, the SE potential of nitro could be six times greater than gas.

Compared to methanol, nitro's theoretical SE advantage is nearly 40 percent at stoichiometric and more than 110 percent at theoretical max power ratios. When you add in nitro's high heat of vaporization (about twice that of methanol), you also get a significant cooling effect in the chamber. Since nitro wants to explode instead of burn in a controlled manner like a properly tuned gasoline-fueled engine, anything you do to reduce chamber hot spots is critical!

All this still doesn't take into account that at extremely rich ratios, the nature of nitro's chemical reaction under combustion changes, producing new end products including hydrogen-another compound that really likes to go "boom" (remember the Hindenburg?).

Although it's possible to run 100 percent nitro-Art Chrisman is said to have done so, with carburetors to boot-experts like Gene Adams don't recommend it. "Even if the rules allow it," Adams says, "cutting nitro with another fuel makes the car more consistent. It'll run cleaner and there's less tendency to drop cylinders. In my experience 98 percent is best overall."

Methanol Brews

Methanol remains the most popular fuel used to cut nitromethane, if only because many sanctioning bodies currently ban the alternatives. Nevertheless, there's a good reason to cut nitro with up to 10 percent methanol: It helps suppress detonation. Ray Hill Turbo recommends a 2.5 percent water/7.5 percent methanol cut to reduce both preignition and detonation tendencies with, it claims, "almost the full power capability of undiluted nitromethane."

Nitro doesn't mix with gasoline-they separate, with the gas on top
Initial start-up with high nitro concentrations is very tricky. Jeff Prock says, "You must get the engine cycling. It won't start up spinning at 200 rpm like a gas engine would. You need to get some heat in the engine and spin it at 1,800 to 2,000 rpm." There's so much fuel pouring into the cylinders that failure to get the engine spinning fast enough before controlled ignition can hydro-lock the engine, or even blow a head off. The common practice is to start and warm up the engine on gas or alcohol.

Once you get a nitro engine going, it may not want to stop. At 7,500 rpm on the top end, there's so much heat in the engine it may keep running under autoignition even if you shut off the magnetos. Essentially, it becomes a diesel. Fuelers today shut down by turning off the fuel pumps as well as the ignition.

Don't Get Mixed Up

Correctly lending nitro involves far more than a mixing cup. The specific gravity (SG) of fuels varies per batch and purity; methanol's out-of-the-barrel concentration can vary 5 percent or so. The by-weight mixture is also dependent upon temperature, both during the initial mix as well as if the temperature changes afterward. As temperature rises, the weight (as measured by SG) decreases. For tuning, it's the percentage by weight that's important, so it is necessary to mix the fuel using a hydrometer and keep track of mixture temperature.

"Nitro engines require lower compression ratios. Normally aspirated with modern race gas or methanol, 15:1 compression ratios are typical. With nitro, you're looking at about 10 to 11:1. A blown motor might run 6.0:1 compression with nitro, 8.5:1 with gasoline, and 12.0 to 13.0:1 on alcohol.

Running Out of Timing

Popularly, nitro is considered a "slow-burning" fuel, but the burn rate is between gas and methanol. The problem is that on high end, nitro-fueled engines, only about 10 percent of the fuel in the chamber is vapor when the burn starts; the rest is liquid. The vapor burns first, which ideally creates enough heat to vaporize the rest of the fuel. But it takes time to create that heat-hence the great amount of lead needed, about twice what you'd use with an equivalent gasoline-fueled engine. Adams says, "Normally aspirated we usually run 60 degrees of lead or 50 degrees with a supercharger. A gasoline-fueled, normally aspirated Hemi might only need 27 to 28 degrees."

Hammered

Nitromethane is weird stuff. You can strike a match next to a puddle of it and nothing will happen. But Jeff Prock says-based on personal experience when he was a kid-if you put a few drops of it on an anvil and hit it with a hammer, there will be a small explosion, somewhat akin to an old cap going off in a toy gun. More seriously, that means you don't want to risk dropping barrels off a truck. The explosion chance is remote, but it is possible, especially on a hot day.

http://www.hotrod.com/how-to/engine/...ethane-anyway/
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