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Re: Will an EMD 2 stroke run away like a Detroit?
Author: SP5103
Date: 02-04-2012 - 12:22
The EMD overspeed system is pretty straight forward. Once it trips, a cam rotates just under the cam shaft. It hits a spring lever which catches the injector rocker arm on its next downstroke and prevents it from following the cam. Since EMD uses unit injection, if the injector rocker arm isn't moving, it can't inject fuel - regardless of the injector rack or governor action. I did get an overspeed trip once when throttle changes and wheelslip got the governor confused and it didn't catch the rpms in time.
A Cooper-Bessemer FWL-6T (like on a GE 70 or 95 ton) has a very different arrangement. Spring tension actually tries to default the rack to full fuel position. The Woodward UG-8 governor has a shut-down solenoid in it, which must be energised to keep the engine running. If you increase the throttle position, you can get a good blast of black smoke from turbo lag. There is a dash-pot connected to the fuel linkage. Poperly adjusted, a check and needle-valve adjustment is used to limit how fast the rack increases, but allows it to decrease without restriction. An overspeed trip does two things - it turns off the fuel pump and governor solenoid, and it also trips an air valve that charges an air cylider in the bottom of the dash pot to force the fuel linkage to the no fuel position. A jammed fuel rack will result in a runaway engine. Hopefully the engine stays together until the fuel in the manifold is used up with the fuel pump off.
As the good Dr. said, Cooper-Bessemer and Alco use the jerk pump system by Bendix. The pushrod running off the cam pumps the fuel, the amount determined by the rack position, but the injector nozzle in the haed is conencted to the pump by steel high pressure tubing. On the FWL-6T, I have seen several arrangements where this tube is either inside or outside the valve cover. Inside and you quickly get fuel dilution of the lube oil (also a common problem on EMD if any of the fuel lines are loose or the injector is leaking). If the injector line is utside the valve cover, then you have the possibility of spraying fuel all over a hot engine. I have seen a C-B that had bad fuel pumps and injector issues that was putting excess fuel in a cylinder. This excess fuel did burn in the exhaust sytem resulting in "flaming pumpkins" coming out of the turbo stack.
I haven't had to argue with an FDL, so I don't know how much of the Cooper-BEssemer fuel control carried over.
With either EMD or C-B, there is no warning light or alarm if the overspeed trips. It is just something you have to check the indicator and manually reset it.
A Cooper-Bessemer FWL-6T (like on a GE 70 or 95 ton) has a very different arrangement. Spring tension actually tries to default the rack to full fuel position. The Woodward UG-8 governor has a shut-down solenoid in it, which must be energised to keep the engine running. If you increase the throttle position, you can get a good blast of black smoke from turbo lag. There is a dash-pot connected to the fuel linkage. Poperly adjusted, a check and needle-valve adjustment is used to limit how fast the rack increases, but allows it to decrease without restriction. An overspeed trip does two things - it turns off the fuel pump and governor solenoid, and it also trips an air valve that charges an air cylider in the bottom of the dash pot to force the fuel linkage to the no fuel position. A jammed fuel rack will result in a runaway engine. Hopefully the engine stays together until the fuel in the manifold is used up with the fuel pump off.
As the good Dr. said, Cooper-Bessemer and Alco use the jerk pump system by Bendix. The pushrod running off the cam pumps the fuel, the amount determined by the rack position, but the injector nozzle in the haed is conencted to the pump by steel high pressure tubing. On the FWL-6T, I have seen several arrangements where this tube is either inside or outside the valve cover. Inside and you quickly get fuel dilution of the lube oil (also a common problem on EMD if any of the fuel lines are loose or the injector is leaking). If the injector line is utside the valve cover, then you have the possibility of spraying fuel all over a hot engine. I have seen a C-B that had bad fuel pumps and injector issues that was putting excess fuel in a cylinder. This excess fuel did burn in the exhaust sytem resulting in "flaming pumpkins" coming out of the turbo stack.
I haven't had to argue with an FDL, so I don't know how much of the Cooper-BEssemer fuel control carried over.
With either EMD or C-B, there is no warning light or alarm if the overspeed trips. It is just something you have to check the indicator and manually reset it.
