Hi
I don't mean to minimize what you are doing and if you or someone can actually figure out a way to really build a miniature diesel fuel injection system it would be an awesome model. However given the high pressures involved and the accuracy required it is going to bea daunting task.
In order to get atomization of the fuel you will need to push it through one or more very small orifices, on conventional full scale direct injection engines these orifices can vary between 4 thousands of an inch to 12 thousands of an inch. Injector opening pressures range from 120 bar up. Precombustion chamber engines are less fussy about atomization due to the confining of the hot air created during compression and can use glow plugs to help initiate combustion during starting. During the diesel cycle you only have a few degrees of crank travel to accomplish atomization and mixing of the fuel with the air. For a direct injection engine typically injection will have to be begin between 20 and 30 degrees before top dead center and combustion should initiate before top dead center. Beginning of combustion will depend speed of the engine low speed engines are more forgiving. When you accomplish this the pressure in the system will rise very rapidly a thousand bar or more is not uncommon. The very high pressures are why steel injection lines are used and the internal bore of these lines will be in the order of one or one and a half millimeters. Not only do the lines have to be strong enough to withstand the pressures, without appreciable expansion, but the fuel will compress slightly at the pressures generated in the system during injection. There are five things that any diesel fuel injection system must accomplish and these are. Meter the quantity of fuel very accurately. Distribute the fuel to the correct cylinder/injector on multi cylinder engines. Control the rate of injection so that the fuel is very rapidly delivered to the injector, this is accomplished by the injection pump cam profile, complete injection within ten or so degrees of engine rotation. Atomize the fuel into micro droplets so that it is easily vaporized by the hot swirling air within the engine cylinder. And finally injection must take place at exactly the right time to insure complete mixing ignition and burning of the fuel during the last few degrees of the compression stoke and the first part of the power stroke. MDCAT. To this, of course the injection pump itself must be capable of generating the kinds of pressures required. A method of preventing the fuel from rushing back into the pump at the end of injection is required and this component is known as a delivery valve which prevents drain back and also prevents secondary injection caused by pressure waves travelling back and forth in the line after the injector closes. Secondary injection is like water pipes banging when a kitchen tap is closed very quickly and there is a lose pipe in the wall.
You didn't mention how you were obtaining turbulence in your engine cylinder. Turbulence is vital to completely mix the fuel with the hot air created during compression. Piston design is the most common way to generate turbulence in direct injection engines. Precombustion,and turbulence chambers or energy cells were used on someengines manufactured up until the last decade of the last century. Prechambers allowed designers to build lighter engines and use lower injection pressures. Examples include the VW Golf, Smaller Ag tractors, GM and Ford Pick up trucks. Prechambered engines did not meet the emission standards of the 21st century and are becoming museum pieces.
This is a rather long ramble which I hope will be taken in the way it was intended as an answert to your question.
Again I don't mean to rain on your parade. Keep at it.
Ernie Johnson
I don't mean to minimize what you are doing and if you or someone can actually figure out a way to really build a miniature diesel fuel injection system it would be an awesome model. However given the high pressures involved and the accuracy required it is going to bea daunting task.
In order to get atomization of the fuel you will need to push it through one or more very small orifices, on conventional full scale direct injection engines these orifices can vary between 4 thousands of an inch to 12 thousands of an inch. Injector opening pressures range from 120 bar up. Precombustion chamber engines are less fussy about atomization due to the confining of the hot air created during compression and can use glow plugs to help initiate combustion during starting. During the diesel cycle you only have a few degrees of crank travel to accomplish atomization and mixing of the fuel with the air. For a direct injection engine typically injection will have to be begin between 20 and 30 degrees before top dead center and combustion should initiate before top dead center. Beginning of combustion will depend speed of the engine low speed engines are more forgiving. When you accomplish this the pressure in the system will rise very rapidly a thousand bar or more is not uncommon. The very high pressures are why steel injection lines are used and the internal bore of these lines will be in the order of one or one and a half millimeters. Not only do the lines have to be strong enough to withstand the pressures, without appreciable expansion, but the fuel will compress slightly at the pressures generated in the system during injection. There are five things that any diesel fuel injection system must accomplish and these are. Meter the quantity of fuel very accurately. Distribute the fuel to the correct cylinder/injector on multi cylinder engines. Control the rate of injection so that the fuel is very rapidly delivered to the injector, this is accomplished by the injection pump cam profile, complete injection within ten or so degrees of engine rotation. Atomize the fuel into micro droplets so that it is easily vaporized by the hot swirling air within the engine cylinder. And finally injection must take place at exactly the right time to insure complete mixing ignition and burning of the fuel during the last few degrees of the compression stoke and the first part of the power stroke. MDCAT. To this, of course the injection pump itself must be capable of generating the kinds of pressures required. A method of preventing the fuel from rushing back into the pump at the end of injection is required and this component is known as a delivery valve which prevents drain back and also prevents secondary injection caused by pressure waves travelling back and forth in the line after the injector closes. Secondary injection is like water pipes banging when a kitchen tap is closed very quickly and there is a lose pipe in the wall.
You didn't mention how you were obtaining turbulence in your engine cylinder. Turbulence is vital to completely mix the fuel with the hot air created during compression. Piston design is the most common way to generate turbulence in direct injection engines. Precombustion,and turbulence chambers or energy cells were used on someengines manufactured up until the last decade of the last century. Prechambers allowed designers to build lighter engines and use lower injection pressures. Examples include the VW Golf, Smaller Ag tractors, GM and Ford Pick up trucks. Prechambered engines did not meet the emission standards of the 21st century and are becoming museum pieces.
This is a rather long ramble which I hope will be taken in the way it was intended as an answert to your question.
Again I don't mean to rain on your parade. Keep at it.
Ernie Johnson
