Phil Cole
Veteran
Location: Redwood City CA
| Nitromethane is a fuel, just like methanol or gasoline. It needs oxygen to burn.
It is used when you want power and don't care about fuel consumption.
The reason is that the air/fuel ratio for nitro is around 1.5/1. For methanol, the air/fuel ratio is 6/1 or so, and for gasoline it's 13/1.
Engines are limited by the amount of air they can cram into the cylinders. You can burn four times as much nitro as methanol in a given engine. The fuel consumption also goes up by four times. This is why you have to run richer when using more nitro.
The energy per pound in the fuels also varies. Gasoline is best at around 19000BTU/lb. Methanol is around 10000 BTU/lb. Nitro is 5200 BTU/lb. This means you don't get four times the power when using nitro, compared to methanol. It's around two times:
For each lb of air you can burn 0.16 lb of methanol, or 0.66 lb of nitro. 0.16 lb of methanol gives you 0.16 x 10000 = 1666 BTU.
0.66 lb of nitro gives you .66 x 5200 = 3466 BTU.
There are other things like the heat of vapourisation that affect the power output so the numbers above won't be reflected in dyno results, but the principles hold.
You can add extra oxidiser as well, if the racing regulations allow it. Nitrous oxide is typically used for this. This simply allow you to burn more fuel than you could just using air. |
