Engine/Transmission (1998.5 - 2002) Combustion process?

[BTowler]

Can someone explain to me how we achieve combustion at startup if the Cummins does not have glowplugs?

 

[Mundgyver]

Fuel will be injected into the cylinder at compression and since the compressed air is around 800 F, the fuel ignights all by itself

 

[Devan Manis]

intake heaters

intake heaters help also

 

[bmoeller]

The grids heaters on the Cummins, serve the same purpose as the glowplugs on the Ford and GM diesels.

 

[gtobey]

In a "compression-ignition" engine, the engine compression has to be high enough that the air being compressed in each cylinder is heated so that when the atomized fuel is injected into this heated air that it will ignite. On a cold engine, the trick is to reach that point without very much temperature loss from the compressed air to the cool surfaces of the cylinder, head, block, etc. , so that combustion temperature can be reached. The starter has the job of cranking the engine fast enough for the cylinders to make the compressed air reach the combustion temperature at the same time the atomized fuel is injected. If all this occurs at the right time and in the correct order, ignition will occur, continue, and the engine should run. Our grid heaters assist this process by raising the temperature of the incoming air so that it will reach combustion temperature a bit more easily, especially with low or sub zero ambient intake air temperature. These grid heaters also help satisfy the EPA requirements of reducing "white smoke" or unburned hydrocarbon emissions during engine warm-up.



The advantage of the "electronically controlled" engine is that the fuel injection timing can be electronically adjusted to inject the atomized fuel at the precise point of maximum cylinder temperature for easier starting and allowing the atomized fuel to mix thoroughly with the compressed air molecules for more complete combustion during engine warm-up. The "timing advance" can also maximize injection timing for light loads part-throttle operation, heavy loads wide-open-throttle operation, and also during high engine RPMs when the fuel must be injected a little earlier in the combustion cycle in order to burn more completely and produce the maximum possible power.



With the P7100 "in-line pump", injection timing is fixed and has no "timing advance", and therefore the basic "static pump to engine timing" has to be compromised to find the "optimum compromise" point to get as much power as possible out of the engine, but also allowing for easy starting.



Everyone is correct. In a nutshell, that's what happens. Certainly not a technical dissertation or a complete scientific explanation, but I hope it will help...

 

[TJany]

compression is what makes a diesel fire. if i remember correctly, 14:1 is the minimum theoretical compression, and our trucks are running 17. 5:1 ? the compression heats the air in the cylinders to a high enough temperature for the fuel to ignite. glow plugs on a ford or chevy are not used during normal operation, only starting, and serve the same purpose as the grid heaters on a cummins. the compression ratio is the ratio of the volume of the cylinder between bottom dead center and top dead center, or in simpler terms, the amopunt the air in the cylinder is being compressed.



as i said b4, the glow plugs have nothing to do with combustion under normal operating circumstances, only during startup.



Tim

 

[tgee]

Grid heaters are great, far less chance of failing because they are located in the intake, not in the combustion chamber. Glow plugs live a hard life. Cant tell you how many glow plug systems I've seen fail.