Why do Diesel Engines Idle in the Cold Weather?

[Randy Stahl]

Let us not forget the most important reason, to keep the cabs warm, so the toliets don't freeze.

Nick

That can get ugly !!! Especially if they have the Microphor toilets!

[nbrodar]

Let us not forget the most important reason, to keep the cabs warm, so the toliets don't freeze.

Nick

[Railway Man]

I believe that Diesel fuel has a higher freezing point then gas. #2 turns to jelly if left in superlow temperatures, so there's actually a heater in the fuel tank or some such and by running the engine it doesn't get a chance to gel up.

 

I may be full of it on that though. 

No, you're very close.  There are 3 main worries.  One is the coolant freezing.  Antifreeze isn't generally practical in EMD and GE engines because of how likely water leaks are versus the damage caused when antifreeze gets in the lube oil.

The two other reasons are the fuel.  Diesel fuel has two critical temps to worry about - the cloud point and the pour point.  The cloud point is the temp where parafin (wax) in the fuel crystalizes.  You can spec the cloud point to be lower in the winter, but it'll cost you more for the fuel.  The fuel will still flow, but the parafin crystals will clog the fuel filter.

The pour point is the temp the fuel turns to a gel and won't flow at all.  You can spec the pour point, too, but the lower you spec it, the more it costs you.  The most common method refiners use to reduce the pour point is blending with #1 fuel oil (kerosene and/or jet fuel).

Even with the engines left idling, keeping the fuel system happy requires some technology.  The engines all have fuel pumps that supply a steady flow to the engine with significant return to the tank, even when in notch 8.  This flow is warmed by passing thru the injectors (high pressure pump on GEs) before going back to the tank.  In very cold climates, this is not enough to keep the fuel in the tank above the cloud point, so most road use fuel preheater which are heat exchangers between the fuel suppy line (upstream of the filters) and the engine cooling system.  UP also uses a "hot well" partition in the fuel tank to keep the fuel near the suction line warm.  The fuel return line is directed to the hot well.

There actually is a fourth worry.  A stone cold engine is difficult to start.  Not because of cold lube oil or fuel so much as lousy combustion. You can either specify high cetane rating or use ether to assist.  One is expesive and the other can be dangerous and risky.

The autostart and APU systems are the current state of the art with regard to cold weather shutdown.

Mr. Dictionary:

How's does Alaska Railroad keep it's fuel tanks from freezing at -20F {Outside}?

My, how arrogant.  But never matter.  The system as described works the same.  And by the way, operating temperature in Alaska is -60F.

RWM

[chefjavier]

I believe that Diesel fuel has a higher freezing point then gas. #2 turns to jelly if left in superlow temperatures, so there's actually a heater in the fuel tank or some such and by running the engine it doesn't get a chance to gel up.

 

I may be full of it on that though. 

No, you're very close.  There are 3 main worries.  One is the coolant freezing.  Antifreeze isn't generally practical in EMD and GE engines because of how likely water leaks are versus the damage caused when antifreeze gets in the lube oil.

The two other reasons are the fuel.  Diesel fuel has two critical temps to worry about - the cloud point and the pour point.  The cloud point is the temp where parafin (wax) in the fuel crystalizes.  You can spec the cloud point to be lower in the winter, but it'll cost you more for the fuel.  The fuel will still flow, but the parafin crystals will clog the fuel filter.

The pour point is the temp the fuel turns to a gel and won't flow at all.  You can spec the pour point, too, but the lower you spec it, the more it costs you.  The most common method refiners use to reduce the pour point is blending with #1 fuel oil (kerosene and/or jet fuel).

Even with the engines left idling, keeping the fuel system happy requires some technology.  The engines all have fuel pumps that supply a steady flow to the engine with significant return to the tank, even when in notch 8.  This flow is warmed by passing thru the injectors (high pressure pump on GEs) before going back to the tank.  In very cold climates, this is not enough to keep the fuel in the tank above the cloud point, so most road use fuel preheater which are heat exchangers between the fuel suppy line (upstream of the filters) and the engine cooling system.  UP also uses a "hot well" partition in the fuel tank to keep the fuel near the suction line warm.  The fuel return line is directed to the hot well.

There actually is a fourth worry.  A stone cold engine is difficult to start.  Not because of cold lube oil or fuel so much as lousy combustion. You can either specify high cetane rating or use ether to assist.  One is expesive and the other can be dangerous and risky.

The autostart and APU systems are the current state of the art with regard to cold weather shutdown.

Mr. Dictionary:

How's does Alaska Railroad keep it's fuel tanks from freezing at -20F {Outside}?

[Anonymous]

I really do hate having to get out of my nice warm switcher to go around and start all the engines around our shop when it starts to get cold, but in turn i also hate having to put them back in the shop because trhey got too cold and dumped their water.

 

[oltmannd]

I believe that Diesel fuel has a higher freezing point then gas. #2 turns to jelly if left in superlow temperatures, so there's actually a heater in the fuel tank or some such and by running the engine it doesn't get a chance to gel up.

 

I may be full of it on that though. 

No, you're very close.  There are 3 main worries.  One is the coolant freezing.  Antifreeze isn't generally practical in EMD and GE engines because of how likely water leaks are versus the damage caused when antifreeze gets in the lube oil.

The two other reasons are the fuel.  Diesel fuel has two critical temps to worry about - the cloud point and the pour point.  The cloud point is the temp where parafin (wax) in the fuel crystalizes.  You can spec the cloud point to be lower in the winter, but it'll cost you more for the fuel.  The fuel will still flow, but the parafin crystals will clog the fuel filter.

The pour point is the temp the fuel turns to a gel and won't flow at all.  You can spec the pour point, too, but the lower you spec it, the more it costs you.  The most common method refiners use to reduce the pour point is blending with #1 fuel oil (kerosene and/or jet fuel).

Even with the engines left idling, keeping the fuel system happy requires some technology.  The engines all have fuel pumps that supply a steady flow to the engine with significant return to the tank, even when in notch 8.  This flow is warmed by passing thru the injectors (high pressure pump on GEs) before going back to the tank.  In very cold climates, this is not enough to keep the fuel in the tank above the cloud point, so most road use fuel preheater which are heat exchangers between the fuel suppy line (upstream of the filters) and the engine cooling system.  UP also uses a "hot well" partition in the fuel tank to keep the fuel near the suction line warm.  The fuel return line is directed to the hot well.

There actually is a fourth worry.  A stone cold engine is difficult to start.  Not because of cold lube oil or fuel so much as lousy combustion. You can either specify high cetane rating or use ether to assist.  One is expesive and the other can be dangerous and risky.

The autostart and APU systems are the current state of the art with regard to cold weather shutdown.

[Dakguy201]

The newest engines monitor their coolant temperature, the brake air pressure and such, and will start themselves should one of the variables fall below the prescribed minimum.  They will then run until everything is back to the prescribed levels and shut themselves off.  Warning lables on these engines warn that they may start unexpectedly, and there is also a buzzer that indicates the engine is about to come to life. 

[Rodney Beck]

The engine is left idleing because (1) they do not have anti-freeze, (2) the cost of fuel is cheap compaired to haveing a locomotive down for freeze up i.e. the engine block could crack and the whole engine has to be replace.

 

Rodney

 

[YoHo1975]

I believe that Diesel fuel has a higher freezing point then gas. #2 turns to jelly if left in superlow temperatures, so there's actually a heater in the fuel tank or some such and by running the engine it doesn't get a chance to gel up.

 

I may be full of it on that though. 

[MontRailLink]

Some friends and I were talking about diesel engines and one was surprised to hear that diesel engines remain idling during cold weather with the recent price of fuel.  When questioned we thought that the answer was due to several factors such as:  1.  Diesel engines don't have anti-freeze so they'd freeze up if not kept running and 2. Diesel engines in cold weather are hard to start due to cold oil in the sump.  Can any of you confirm/deny the reasons stated above for keeping diesel engines idling in cold weather or add any others we may not know about.  Thanks.