Power is produced by burning fuel. Add more fuel and enough air to burn that fuel, and the engine will produce more power. While the diesel engine fuel/air ratio isn't as critical as it is when tuning a gasoline engine, the ratio still needs to be kept reasonable to prevent overfueling and locomotive levels of black smoke.
Earth's atmosphere contains approximately 21% oxygen - a critical element in internal combustion. Adding more oxygen to the combustion process allows for more fuel, thus increasing the thermal energy available to the engine. Turbochargers have long been used to add oxygen, by increasing manifold pressure. Up to a point, turbochargers are efficient and help to provide the necessary power increase that diesel owners are looking for. However, once past a certain level of boost pressure, the efficiency of the turbo and intercooler is overcome by increasing levels of heat accompanying higher boost pressures.
An overfueled diesel engine will produce an unacceptable level of black smoke. One popular solution is to add nitrous oxide gas to the intake air. Properly set up, nitrous can add somewhere between 50 and 150 additional horsepower along with a big reduction in black smoke.
Nitrous oxide provides two important benefits when injected into the intake system of a diesel engine. 1- Added oxygen: Nitrous oxide gas contains approximately 37% oxygen, greatly increasing the amount of oxygen available to the combustion process. 2- Cooler intake air temperatures: The transition from a high pressure liquid nitrous bottle through a small nozzle to a much lower intake manifold pressure greatly reduces the intake air temperature. Cooler intake air increases air density, which allows for more oxygen molecules to be packed into the same volume.
Before moving on, I should point out that nitrous oxide injection is useful primarily for competition - situations that require short bursts of power, such as running for 10-15 seconds on a dyno, truck sled pull events or at the 1/4-mile track. Here, nitrous can help provide a huge % power gain. Nitrous is not very useful for RV'ers or heavy haulers.
Nitrous kits come with a selection of jets that can be used to fine tune the amount of injected nitrous. Experienced nitrous users recommend first installing a power module that overfuels the engine to some degree, producing excessive amounts of black smoke. Then, begin with a 40-50 size nitrous jet to see what effect it has on the black smoke. The level of black smoke should decrease as you add more nitrous through larger and larger jets - incrementing upward in units of ten (i.e. 50, 60, 70, etc.). Racers I've spoken to use 50 to 120 size jets, depending on how much power they're making. Gains anywhere from 50 to 400HP are possible
Making big power these days requires help to burn all of the fuel provided by the power modules and programs used in competition, and nitrous helps burn that fuel and make more power. Adding more nitrous than necessary doesn't appear to harm anything, but can actually decrease performance by over-cooling the combustion temperatures. There appears to be quite a wide latitude in the amount of spray that works for people, but performance testing is the best way to know for sure. See you at the track!
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