You’re correct, drums are certainly not trouble free, but imagine a drum getting hotter than it should under braking due to (perhaps) other brakes under performing, then the drum will expand away from the shoes. On the other hand the brake pads on a disk brake set up can’t expand away from the disk. As the disk gets hotter and hotter, the pad to disk clearance diminishes so the pads go tighter against the disk, getting hotter and hotter.
Only takes a sticking slide pin on a calliper for the disk to start getting hot.
I personally don’t think more trucks are catching fire these days. It’s very easy to put dash cams, mobile phones footage onto social media, years ago nobody carried a video camera or camera and if they did it would be old news by the time they got the footage developed.
Moose:
I think they still catch fire faster and more easily nowadays, having seen in real life and on film, as well of knowing of someone that died in a fire after a crash.
The fact is the temperatures are higher and the diesel tank is still a thin grade of either alloy or steel as has been the case for many years!
There are a lot of plastic fuel tanks out there as well
Bluey Circles:
Cosmic:
With a traditional system the temperature of the pipes will very rapidly fall (maybe within a minute) to below the auto ignition temperature of diesel which I think is around 250C. In fact I could imagine that diesel coming into contact with the hot pipes would cool them so rapidly they would quickly loose the potential to ignite the diesel.
However as mention above the massive bulk of the DPF will hold its temperature well, it may be staying above the 250 dergee temperature long enough to ignite any diesel coming into contact with it.
The regeneration process will take the temperature of the exhaust up to somewhere between 600 & 700 degrees, if you want to cool pipes down from around the 250o area petrol would be the best option it will not ignite, Diesel on a manifold at about 200o & upwards will ignite instantly.
Dave.
dave docwra:
Bluey Circles:
Cosmic:
With a traditional system the temperature of the pipes will very rapidly fall (maybe within a minute) to below the auto ignition temperature of diesel which I think is around 250C. In fact I could imagine that diesel coming into contact with the hot pipes would cool them so rapidly they would quickly loose the potential to ignite the diesel.
However as mention above the massive bulk of the DPF will hold its temperature well, it may be staying above the 250 dergee temperature long enough to ignite any diesel coming into contact with it.The regeneration process will take the temperature of the exhaust up to somewhere between 600 & 700 degrees, if you want to cool pipes down from around the 250o area petrol would be the best option it will not ignite, Diesel on a manifold at about 200o & upwards will ignite instantly.
Dave.
600 - 700 Fahrenheit or Centigrade ? if it was the latter it would be glowing dark red in colour, or are you meaning the temp deep inside the contraption.
I had problems with a DPF and attached a high temp probe to the outside to try and work out what was going on. Regen seemed to produce the same temperature as when ascending a big hill, around 350 Centigrade, and this would be the same temp that I would achieve with a tradition exhaust (just downstream from turbo)
The big difference I noted from traditional exhaust to DPF is the cooling. Ascend a big hill and it will go up to 350c. With a traditional exhaust this would fall back to just above a 100c on descending the other side of the hill on the over-run. With the DPF fitted it could still be cooking away at 200+c
Interestingly, and heading way off topic, if you want to get a DPF hot, go up a big hill, wellying it on the motorway just does not create the same temperatures, and I also noted going up a big hill slowly produces higher temperatures than going up as fast as possible (maybe it has more time to heat up?) you also get a dam site more mpg without the hateful things fitted.
BC you are right about hills & motorways but neither on there own can normally generate enough heat for a burn, the ECU alters the fueling system & parameters to generate the heat, I have done a few manual regens and the down pipe indeed starts to change colour to a deep red.
dave docwra:
BC you are right about hills & motorways but neither on there own can normally generate enough heat for a burn, the ECU alters the fueling system & parameters to generate the heat, I have done a few manual regens and the down pipe indeed starts to change colour to a deep red.
So it must be 600+C if it is going that colour, that is seriously hot.
But is regen not the last resort the engine utilises when the DPF is becoming blocked. I was under the impression that regen would never be needed if the engine was regularly getting run at full temperature. Its too much town centre driving that is the big problem, at little more than tick over the manifold and down pipes can fall to under a 100c and this is when they start to clog up with soot.
Roymondo:
In years gone by, diesel was drawn by a pump on the engine sucking it through the fuel lines. Rupture the line and the pump starts drawing fresh air. On modern trucks the fuel is pumped at high pressure TO the engine. Rupture the line and fuel sprays out in just the right form (fine mist) to be ignited by a handy spark.Sent using smoke and mirrors
This.
Sent from my SM-G900W8 using Tapatalk
Bluey Circles:
dave docwra:
BC you are right about hills & motorways but neither on there own can normally generate enough heat for a burn, the ECU alters the fueling system & parameters to generate the heat, I have done a few manual regens and the down pipe indeed starts to change colour to a deep red.So it must be 600+C if it is going that colour, that is seriously hot.
But is regen not the last resort the engine utilises when the DPF is becoming blocked. I was under the impression that regen would never be needed if the engine was regularly getting run at full temperature. Its too much town centre driving that is the big problem, at little more than tick over the manifold and down pipes can fall to under a 100c and this is when they start to clog up with soot.
All the ones I have done have been used in a city enviroment plodding about all day, The first thing I have to do before carrying out a forced regen is clear the area around the vehicle to avoid a fire, the smoke & the heat coming from the exhaust is unbelievable as it gets up to temperature.
Dave…
I think you will find that in most cases the diesel is still drawn from the tank not at "high pressure " but at high volume, the pressurisation takes place via the injectors, (at this time I can only think of DAF that use individual pumps per injector) then what’s not been used returns to the tank also at quite high volume and at quite a high temperature
■■■■■■■ sorted all this out donkeys years ago, most other manufacturers have since followed.
Think about it, fuel pumped from the tank at high pressure through flexible plastic pipes ffs!
The Foden of mine in the pic above is nearly 20 years old and is fitted with the last generation of L10 engine, for those that don’t know the injectors work off the cam which means fuel is at a relatively low pressure until the injectors compress the fuel and inject, as a result much higher pressures can be achieved, which means a cleaner burn, which is what’s required today with modern emissions regulations.
One of the reasons older manufacturers no longer build commercial vehicle engines is that they could not reliably inject fuel at high enough pressure using gear driven pumps and individual injector pipes to meet modern emissions regulations!
Before anyone bangs on about Volvo and Scania neither would be where they are today without help from ■■■■■■■■
There’s still a pump in (or near) the tank, pumping fuel to the engine, regardless of the actual pressure level. It continues to pump even if the fuel lines are ruptured, and the pressure is still several Bar. Many (most?) fuel-injected cars have an inertia switch to kill this pump in the event of a collision precisely because of the fire risk.
Roymondo:
There’s still a pump in (or near) the tank, pumping fuel to the engine, regardless of the actual pressure level. It continues to pump even if the fuel lines are ruptured, and the pressure is still several Bar. Many (most?) fuel-injected cars have an inertia switch to kill this pump in the event of a collision precisely because of the fire risk.
I haven’t seen one yet .only in cars and it’s not several bar .
Moose:
I think you will find that in most cases the diesel is still drawn from the tank not at "high pressure " but at high volume, the pressurisation takes place via the injectors, (at this time I can only think of DAF that use individual pumps per injector) then what’s not been used returns to the tank also at quite high volume and at quite a high temperature
■■■■■■■ sorted all this out donkeys years ago, most other manufacturers have since followed.
Think about it, fuel pumped from the tank at high pressure through flexible plastic pipes ffs!
The Foden of mine in the pic above is nearly 20 years old and is fitted with the last generation of L10 engine, for those that don’t know the injectors work off the cam which means fuel is at a relatively low pressure until the injectors compress the fuel and inject, as a result much higher pressures can be achieved, which means a cleaner burn, which is what’s required today with modern emissions regulations.
One of the reasons older manufacturers no longer build commercial vehicle engines is that they could not reliably inject fuel at high enough pressure using gear driven pumps and individual injector pipes to meet modern emissions regulations!
Before anyone bangs on about Volvo and Scania neither would be where they are today without help from ■■■■■■■■
The old cam operated mechanical injectors went out with the ark.To be replaced with a very high pressure line fed system in which the single feed line ( rail ) accumulates the pressure before the injectors while the injectors are just electronically controlled valves.The end result being the combination of electrics all over the engine and what is effectively a big fuel pipe containing massive fuel pressure.If the pipe gets damaged and leaks and an electric circuit shorts out by damage all the ingredients required are there.IE fuel in a fine high pressure mist and a hot electrical discharge.
I’ve also a Volvo Fh12 fitted with unit injectors, there’s an engine gear driven external pump, which draws fuel from the tank and through the filters and into the cylinder head to the injectors, this is nowhere near injection pressure, the rest is done inside the cam operated injector, the electrics open and close the injector, same as the fh13 fh16 ■■■■■■■ M11 etc!
We’re not talking about Landrover Freelanders and Ford Focus type vehicles here
Moose:
I’ve also a Volvo Fh12 fitted with unit injectors, there’s no external high pressure pump, it done inside the cam operated injector
The D13 seems to be an exception in that regard.They seem to be calling it a common rail hybrid system which seems to combine the advantages of common rail systems with old school cam operated injectors. 
Which seems to be a contradiction but it obviously seems to work.Probably without the questions over the security of an externally pumped pressurised rail and electrically actuated injectors in the event of accidents.
Moose:
I think you will find that in most cases the diesel is still drawn from the tank not at "high pressure " but at high volume, the pressurisation takes place via the injectors, (at this time I can only think of DAF that use individual pumps per injector) then what’s not been used returns to the tank also at quite high volume and at quite a high temperature
■■■■■■■ sorted all this out donkeys years ago, most other manufacturers have since followed.
Think about it, fuel pumped from the tank at high pressure through flexible plastic pipes ffs!
The Foden of mine in the pic above is nearly 20 years old and is fitted with the last generation of L10 engine, for those that don’t know the injectors work off the cam which means fuel is at a relatively low pressure until the injectors compress the fuel and inject, as a result much higher pressures can be achieved, which means a cleaner burn, which is what’s required today with modern emissions regulations.
One of the reasons older manufacturers no longer build commercial vehicle engines is that they could not reliably inject fuel at high enough pressure using gear driven pumps and individual injector pipes to meet modern emissions regulations!
Before anyone bangs on about Volvo and Scania neither would be where they are today without help from ■■■■■■■■
The heat of the fuel return is the one thing I was thinking of that is something that has changed on modern trucks. The tank can get really quite hot.