A
Anonymous
Guest
Oh gosh, where to start...? 
I love this (general) topic, so all my friends out there please forgive me if I run a little long here, eh? :roll: Also, I am suffering from jet-lag. I just got home from a couple of weeks of shuttling Grunts and their stuff from Europe to the Sand Box, and am now home on the West Coast wondering why the sun went down when it should have been coming up, etc. So please forgive me if I come across as even more goofy than normal. 8)
Except for some early diesels that ran on solid hydrocarbons (coal dust, sawdust, peanut shells, etc), no diesels since have been designed to run by detonation. They all run using the same controlled flame front idea as spark ignition engines, it's just that their method of igniting the fuel differs. And in fact, CI engines (technically these are compression ignition engines...the fuel is called "diesel") can be configured to run on any liquid hydrocarbon from alky to axle grease. That includes gasoline, kerosene, methanol, jet fuel, used McDonald's frying oil, diesel, etc. Diesel is the fuel of choice for a variety of reasons, the most important probably being that diesel acts as a lubricant for the mechanical high pressure injector pump typically used in CI engines. Diesel is also very stable, doesn't evaporate readily, and is quite safe to store and handle compared to gasoline. In prior decades, diesel was largely a by-product of the distillation process used to make gasoline, which gave the refineries another product to sell (rather than simply burning it off). Today's refining technologies aren't nearly so dependent on distillation, though, so this is no longer much of a factor. In fact, there is little to choose from between gasoline and diesel for a modern catalytic-based refinery, so they just refine to their immediate market.
As 84_250 explains above, CI engines inject their fuel into air that is already hot enough to ignite the fuel, so combustion starts more or less immediately. Picture it like this. Air enters the cylinder during the intake stroke and the intake valve then closes. The piston now rams upward in a few ten-thousands of a second, compressing the air and heating it at the same time (the very act of compressing air heats it) to more than 900 degrees F. A few degrees before TDC, the injector squirts fuel into this very hot air and the fuel ignites, reaching maximum pressure (this is the point of max torque for the engine) at roughly 15 degrees after TDC.
So far, we are just considering a normally aspirated diesel engine, so let's add more fuel, a turbo, nitrous, and propane in sequence. Diesels make more power to a point of "heavy smoke" as one injects more fuel for the available air. That's why you can melt the piston of a NA diesel by cranking up the fuel delivery. The added heat and pressure inside the combustion chamber can literally melt an aluminum piston, which is why many "old timey" diesels used cast iron pistons -- they could crank up the fuel delivery without destroying the piston. Modern diesels have aluminum pistons and use a turbo to keep temperatures in check. They make more power by adding air and fuel for clean, low temperature combustion without nuking the piston.
Adding air from a turbo or nitrogen and oxygen by injecting nitrous oxide accomplishes the same thing. One is leaning the mixture in a fuel/air ratio sense. Leaning the mixture lowers the temperature of the combustion process in a CI engine. Of course, a turbo adds compressed air, which leads to a temperature rise in and of itself, but not nearly so high as adding dangerously large amounts of fuel without more air. So I am not surprised that the added nitrous made little additional power in this test -- you can accomplish the same thing by simply adding a little turbo boost. The bottom line is that adding more air (by more boost or nitrous or both) allows one to safely add fuel to make more power without melting critical engine parts. Naturally, as one makes more power, additional cooling capacity has to be added as well or all this good work will come undone. We haven't turned physics on its head here after all...
So how does adding propane to the mix help us make more power? Easy, adding a little propane allows us to burn the injected diesel more efficently. This results in more power in and of itself, although there is a little additional power from the propane (but not much if done correctly).
Here's how it works, by fumigating (adding as a gas) propane upstream of the turbo, we assure the propane is evenly distributed to each cylinder by the mixing action of the turbo blades. Propane has an ignition temperature of about 1000 degrees, so won't self-ignite as the piston sweeps up on the compression stroke. However, as soon as the diesel is injected, it ignites, which ignites the propane in turn. The flame front from the propane helps boil off and ignite the tiny diesel proplets being injected into the cylinder, producing more complete combustion and more power per unit of diesel injected.
There you have it, a quick and dirty on some of my favorite engine subjects...
Some additional thoughts, though. Simply making more power won't usually negatively affect an engine, so long as cooling and lubricating requirements are adequately looked after, and RPMs are kept in the safe zone. I imagine that the Izuzu can make plenty more grunt without puking its guts out. More boost and fuel, with appropriate chip programming to account for it, and one can have all the reliable power one wishes for. I'd skip the nitrous, though. It's not "dangerous". It just isn't needed. Simply add more boost and fuel! Why add something that needs frquent replenishing when what you already have on board will work just as well, and doesn't require a run to the speed shop every few weeks?
I love this (general) topic, so all my friends out there please forgive me if I run a little long here, eh? :roll: Also, I am suffering from jet-lag. I just got home from a couple of weeks of shuttling Grunts and their stuff from Europe to the Sand Box, and am now home on the West Coast wondering why the sun went down when it should have been coming up, etc. So please forgive me if I come across as even more goofy than normal. 8)
Except for some early diesels that ran on solid hydrocarbons (coal dust, sawdust, peanut shells, etc), no diesels since have been designed to run by detonation. They all run using the same controlled flame front idea as spark ignition engines, it's just that their method of igniting the fuel differs. And in fact, CI engines (technically these are compression ignition engines...the fuel is called "diesel") can be configured to run on any liquid hydrocarbon from alky to axle grease. That includes gasoline, kerosene, methanol, jet fuel, used McDonald's frying oil, diesel, etc. Diesel is the fuel of choice for a variety of reasons, the most important probably being that diesel acts as a lubricant for the mechanical high pressure injector pump typically used in CI engines. Diesel is also very stable, doesn't evaporate readily, and is quite safe to store and handle compared to gasoline. In prior decades, diesel was largely a by-product of the distillation process used to make gasoline, which gave the refineries another product to sell (rather than simply burning it off). Today's refining technologies aren't nearly so dependent on distillation, though, so this is no longer much of a factor. In fact, there is little to choose from between gasoline and diesel for a modern catalytic-based refinery, so they just refine to their immediate market.
As 84_250 explains above, CI engines inject their fuel into air that is already hot enough to ignite the fuel, so combustion starts more or less immediately. Picture it like this. Air enters the cylinder during the intake stroke and the intake valve then closes. The piston now rams upward in a few ten-thousands of a second, compressing the air and heating it at the same time (the very act of compressing air heats it) to more than 900 degrees F. A few degrees before TDC, the injector squirts fuel into this very hot air and the fuel ignites, reaching maximum pressure (this is the point of max torque for the engine) at roughly 15 degrees after TDC.
So far, we are just considering a normally aspirated diesel engine, so let's add more fuel, a turbo, nitrous, and propane in sequence. Diesels make more power to a point of "heavy smoke" as one injects more fuel for the available air. That's why you can melt the piston of a NA diesel by cranking up the fuel delivery. The added heat and pressure inside the combustion chamber can literally melt an aluminum piston, which is why many "old timey" diesels used cast iron pistons -- they could crank up the fuel delivery without destroying the piston. Modern diesels have aluminum pistons and use a turbo to keep temperatures in check. They make more power by adding air and fuel for clean, low temperature combustion without nuking the piston.
Adding air from a turbo or nitrogen and oxygen by injecting nitrous oxide accomplishes the same thing. One is leaning the mixture in a fuel/air ratio sense. Leaning the mixture lowers the temperature of the combustion process in a CI engine. Of course, a turbo adds compressed air, which leads to a temperature rise in and of itself, but not nearly so high as adding dangerously large amounts of fuel without more air. So I am not surprised that the added nitrous made little additional power in this test -- you can accomplish the same thing by simply adding a little turbo boost. The bottom line is that adding more air (by more boost or nitrous or both) allows one to safely add fuel to make more power without melting critical engine parts. Naturally, as one makes more power, additional cooling capacity has to be added as well or all this good work will come undone. We haven't turned physics on its head here after all...
So how does adding propane to the mix help us make more power? Easy, adding a little propane allows us to burn the injected diesel more efficently. This results in more power in and of itself, although there is a little additional power from the propane (but not much if done correctly).
Here's how it works, by fumigating (adding as a gas) propane upstream of the turbo, we assure the propane is evenly distributed to each cylinder by the mixing action of the turbo blades. Propane has an ignition temperature of about 1000 degrees, so won't self-ignite as the piston sweeps up on the compression stroke. However, as soon as the diesel is injected, it ignites, which ignites the propane in turn. The flame front from the propane helps boil off and ignite the tiny diesel proplets being injected into the cylinder, producing more complete combustion and more power per unit of diesel injected.
There you have it, a quick and dirty on some of my favorite engine subjects...
Some additional thoughts, though. Simply making more power won't usually negatively affect an engine, so long as cooling and lubricating requirements are adequately looked after, and RPMs are kept in the safe zone. I imagine that the Izuzu can make plenty more grunt without puking its guts out. More boost and fuel, with appropriate chip programming to account for it, and one can have all the reliable power one wishes for. I'd skip the nitrous, though. It's not "dangerous". It just isn't needed. Simply add more boost and fuel! Why add something that needs frquent replenishing when what you already have on board will work just as well, and doesn't require a run to the speed shop every few weeks?
