Diesel Polishing

[RaymondR]

Originally Posted by Q Xopa

Hmmm,

I understand the reason fuel spraying out of a leak is not desirable.

Being like yourself of an aviation background, most of aircraft fuel systems are pressurized from the tank.

This will obviously spray fuel onto possibly a hot engine part or arcing set of electrical brushes etc.

The alternitive is to do the sucking from the engine.

Apart from one turbine helicopter I am familiar with, S76, all others have the pressurized fuel from the tanks from boost pumps. In fact most of these fuel boost pumps are switchable on or off by the pilot. So most aircraft can work equally happily pressurized, or suction.

This was the idea of the S76 fuel system to not potentially spray fuel from a leak. All helicopters before and since, that I am aware of have had pressurised fuel systems. Indeed I have never heard of, in my 40 year and counting, an aircraft fire from a fuel leak spray.

I know aircraft also benefit from pressurized fuel to reduce fuel vapor locks at reduced pressure at altitude, which is not a boat concern.

But with diesel engine boats Im not sure if this is a valid concern?

Lets think about a suction fuel filter systems. A leak here goes in not out, sure. But that often means your engine is snuffed as engines dont like trying to run on air. I consider this to be a concern.

Which flavor of fuel leak issue is a bigger concern Im sure is debatable?

The other advantage of a pressrized fuel system is finding the leak. Its much easier to find fuel coming out wet spots than air going in.

Just my 2c.

Volvo were one of the first auto manufacturers to put a fuel pump in the tanks of their cars. They did it to keep the rank slightly under vacuum so that if there was a leak in the tank fuel would not spill and cause a fire.

Obviously Volvo thought that the consequences of a large fuel spill from a ruptured tank were far worse than a leaking fuel line.

[Q Xopa]

Originally Posted by RaymondR

Volvo were one of the first auto manufacturers to put a fuel pump in the tanks of their cars. They did it to keep the rank slightly under vacuum so that if there was a leak in the tank fuel would not spill and cause a fire.

Obviously Volvo thought that the consequences of a large fuel spill from a ruptured tank were far worse than a leaking fuel line.

Ok,

So how many car fuel fires have you heard of from either ruptured tanks or leaky fuel tanks? I have seen plenty on Hollywood movies, but real life never.

So assuming we are talking about diesel fuel systems, I cant see the logic of saying a pressurized fuel system is allowed on cars but not considered 'safe' in boats?

They are considered safe on aircraft, and I would say the consequeces are greater in aircraft.

As far as 'Safe' is concerned, I dont know that suction fuel systems are any safer.

The risks are different.

Fire risk with a pressure system. Sure of course none of us wants a fire.

However practically I dont think this is much of a risk. Have you tried to light diesel? Or heard of this happening?

Engines stopping with a suction fuel system sucking a big gulp of air through a leak? Engineless in a shipping channel or on a lee shore is not a safe possibility either.

I dont know which is the greatest potential peril? My guess would be the latter.

My point is calling a pressure fuel system too unsafe for boats is only half the story.

[noelex 77]

Originally Posted by Q Xopa

However practically I dont think this is much of a risk. Have you tried to light diesel? Or heard of this happening?

Just a slight note of caution.

I always understood that diesel was very difficult to ignite, but since owning a diesel heater I have changed my mind.

The heater just drips diesel fuel into a tray and this is lit with a match or stick lighter. It lights surprisingly easily. I often use a small wad of rolled up paper (about he size of fingernail), but there is no need for any accelerant such as methylated spirits.

Diesel is obviously much safer than petrol, but don’t be lulled into a false sense of security. It burns very nicely and is not hard to ignite.

[Q Xopa]

Originally Posted by noelex 77

Just a slight note of caution.

I always understood that diesel was very difficult to ignite, but since owning a diesel heater I have changed my mind.

The heater just drips diesel fuel into a tray and this is lit with a match or stick lighter. It lights surprisingly easily. I often use a small wad of rolled up paper (about he size of fingernail), but there is no need for any accelerant such as methylated spirits.

Diesel is obviously much safer than petrol, but don’t be lulled into a false sense of security. It burns very nicely and is not hard to ignite.

Agreed you can light it, under certain conditions. It is afterall a fuel.

You basically need a naked flame and small drops. Atomised spray out of an injector ideally. Even better vaporised. But that take a lot of heat.

As is kerosene in aeroplanes with similar burning characteristics.

Its not impossible in an engine bay, Im not suggesting it is.

Maybe you have heard of an actual occurrence? I have not.

Are you saying you consider pressure fuel systems unacceptably dangerous? This is of course your call.

Its all a question of keeping the risks in perspective of risk of an occurrence and the consequences if it does.

The aviation industry consider this an acceptable risk, obviously within all the other industry safety stsndard practises.

What do you consider a greater risk? A pressure or suction fuel system.

I would say its more a question of how well an individual system has been constructed and maintained.

[noelex 77]

Originally Posted by Q Xopa

Agreed you can light it, under certain conditions. It is afterall a fuel.

You basically need a naked flame and small drops. Atomised spray out of an injector ideally. Even better vaporised. But that take a lot of heat.

I think it is important to understand that diesel can be ignited quite easily with a simple small flame. The diesel does not have to meet any special requirements such as being present in droplet or atomised form.

Lighting our diesel heater involves igniting a small tray (about the size of saucer) that has been filled with ordinary diesel.

I was mistakenly under the impression that it is quite hard to start a fire in a pool of diesel. Lighting our diesel heater involves doing just this and it is not hard at all.

[s/v Jedi]

Originally Posted by noelex 77

I think it is important to understand that diesel can be ignited quite easily with a simple small flame. The diesel does not have to meet any special requirements such as being present in droplet or atomised form.

Lighting our diesel heater involves igniting a small tray (about the size of saucer) that has been filled with ordinary diesel.

I was mistakenly under the impression that it is quite hard to start a fire in a pool of diesel. Lighting our diesel heater involves doing just this and it is not hard at all.

I’m sure others can explain this in detail but there must obviously be a difference between lighting the fuel cup of the heater and a pool of diesel. There are plenty demonstrations showing that throwing a lighted match into the pool does not ignite the diesel. Also, throwing diesel into a fire makes it flame up. I think it may be the temperature with the cup being so shallow that you can heat the diesel to combustion temperature while a bigger volume has too much thermal mass ?

[a64pilot]

Originally Posted by Q Xopa

Hmmm,

I understand the reason fuel spraying out of a leak is not desirable.

Being like yourself of an aviation background, most of aircraft fuel systems are pressurized from the tank.

This will obviously spray fuel onto possibly a hot engine part or arcing set of electrical brushes etc.

The alternitive is to do the sucking from the engine.

Apart from one turbine helicopter I am familiar with, S76, all others have the pressurized fuel from the tanks from boost pumps. In fact most of these fuel boost pumps are switchable on or off by the pilot. So most aircraft can work equally happily pressurized, or suction.

This was the idea of the S76 fuel system to not potentially spray fuel from a leak. All helicopters before and since, that I am aware of have had pressurised fuel systems. Indeed I have never heard of, in my 40 year and counting, an aircraft fire from a fuel leak spray.

I know aircraft also benefit from pressurized fuel to reduce fuel vapor locks at reduced pressure at altitude, which is not a boat concern.

But with diesel engine boats Im not sure if this is a valid concern?

Lets think about a suction fuel filter systems. A leak here goes in not out, sure. But that often means your engine is snuffed as engines dont like trying to run on air. I consider this to be a concern.

Which flavor of fuel leak issue is a bigger concern Im sure is debatable?

The other advantage of a pressrized fuel system is finding the leak. Its much easier to find fuel coming out wet spots than air going in.

Just my 2c.

I know of no pressurized fuel systems on turbine helicopters, ones I’m familiar with do have boost pumps used only for starting, the OH-58 when using JP-4 fuel that has been gone for a long time, you turned the boost pump on at altitudes above 10,000 ft. I’m order to prevent vapor lock. JP -8 or Jet -A isn’t a problem.
However there are many Civilian helicopters I have no experience with and some Military.

I know on boats, at least gasoline outboard boats the fuel line is not allowed to be pressurized, leading to some interesting workarounds for fuel injected outboards.
This tank
https://www.boats.net/product/mercur...4aAtaVEALw_wcB
Sits on the back of a Mercury Verado, it has a low and a high pressure pump and a float switch, the float switch and low pressure pump keeps the tank full, the HP pump supplies fuel for the injection system. All that Rune Golburg stuff is so the line has no pressure in it.

[a64pilot]

Originally Posted by noelex 77

I think it is important to understand that diesel can be ignited quite easily with a simple small flame. The diesel does not have to meet any special requirements such as being present in droplet or atomised form.

Lighting our diesel heater involves igniting a small tray (about the size of saucer) that has been filled with ordinary diesel.

I was mistakenly under the impression that it is quite hard to start a fire in a pool of diesel. Lighting our diesel heater involves doing just this and it is not hard at all.

Atomize it from a fuel leak and it’s even easier. As I’ve been burnt when I was younger fire scares me, especially on a boat as it’s hard to run away from it. Of course any fuel it’s not the liquid that’s burning, but the fumes, I believe it’s the higher vapor pressure that makes Diesel harder to ignite, but heat it even just a little and it gets much easier.

[a64pilot]

Originally Posted by s/v Jedi

I’m sure others can explain this in detail but there must obviously be a difference between lighting the fuel cup of the heater and a pool of diesel. There are plenty demonstrations showing that throwing a lighted match into the pool does not ignite the diesel. Also, throwing diesel into a fire makes it flame up. I think it may be the temperature with the cup being so shallow that you can heat the diesel to combustion temperature while a bigger volume has too much thermal mass ?

Thermal mass is irrelevant, it’s not the fuel that’s burning, it’s the vapor. That is why boiling fuel will make such a huge flame, because there is so much more vapor.
First paragraph
https://en.wikipedia.org/wiki/Liquid_fuel

[a64pilot]

Even the combustion cause of a Diesel engine is most often misunderstood, it’s not the heat from compression that initiates the ignition in a running Diesel, it’s the heat left in the combustion chamber from the last ignition event, they only “Diesel” when starting.

And there is no explosion in either a gas or a Diesel either, or there can be initially in a Diesel, that’s the knocking you can hear in a cold one, but under normal running conditions, there is never an explosion.

[noelex 77]

Originally Posted by s/v Jedi

I think it may be the temperature with the cup being so shallow that you can heat the diesel to combustion temperature while a bigger volume has too much thermal mass ?

I suspect, as you have indicated, if the diesel pool is deep or has a large volume, such as a 44 gallon drum of diesel, it is much harder to ignite with a small flame.

The typical depth I introduce into the tray is only a few millimeters (perhaps an 1/8 inch) deep. Think of a cup saucer filled with diesel. The depth of diesel in the tray does not seem particularly important for success, but it cannot be more than perhaps half an inch deep as this is all the tray will hold.

Worryingly, the diesel in the bottom of the heater is very much like I would expect in the bilge from a small fuel spill. The heater has nothing special, no glow plugs, no electric fans, just a tray that you fill with diesel.

[Q Xopa]

Originally Posted by a64pilot

I know of no pressurized fuel systems on turbine helicopters, ones I’m familiar with do have boost pumps used only for starting, the OH-58 when using JP-4 fuel that has been gone for a long time, you turned the boost pump on at altitudes above 10,000 ft. I’m order to prevent vapor lock. JP -8 or Jet -A isn’t a problem.
However there are many Civilian helicopters I have no experience with and some Military.

I know on boats, at least gasoline outboard boats the fuel line is not allowed to be pressurized, leading to some interesting workarounds for fuel injected outboards.
This tank
https://www.boats.net/product/mercur...4aAtaVEALw_wcB
Sits on the back of a Mercury Verado, it has a low and a high pressure pump and a float switch, the float switch and low pressure pump keeps the tank full, the HP pump supplies fuel for the injection system. All that Rune Golburg stuff is so the line has no pressure in it.

Hmm, I started my career on these very same aircraft. And in the intervening years their civilan counterparts. I could be wrong but I would class, with the boost pump on, as you say starting, or at altitude it is a pressurized fuel system. You dont agree? As you say, and I previously said it with a flick of a switch it can also as happily turn into a and operate as a suction fuel system.

I think we are agreeing?

Yes petrol fuel systems are different and not what I was referring to.

[a64pilot]

Originally Posted by Q Xopa

Hmm, I started my career on these very same aircraft. And in the intervening years their civilan counterparts. I could be wrong but I would class, with the boost pump on, as you say starting, or at altitude it is a pressurized fuel system. You dont agree? As you say, and I previously said it with a flick of a switch it can also as happily turn into a and operate as a suction fuel system.

I think we are agreeing?

Yes petrol fuel systems are different and not what I was referring to.

Boost pump is only used for starting, although it’s not really needed, on the AH-64 it was an air driven vane motor turning a pump, a vane would get stuck very frequently, and the crew would never know, the only way to tell was if the brrrr noise was missing when the start switch was engaged.
Eventually it would be noticed and written up, the usual fix was to dump some break free (CLP) down the air supply line, that would most often work, until it got stuck again.

Liquid fuel in a bowl or on the ground etc doesn’t burn, it’s the vapor that does, and if you place some fuel in a cup or something and ignite it and can look at it from the side you will see the flame is above the fuel level. As the liquid heats, it gives off more vapor and the flame gets bigger, if it gets to the boiling point it gets very, very vigorous, Basie of course boiling releases a lot of vapor.

When you atomize fuel its much easier to burn because your tremendously increasing the surface area by breaking it into small droplets, so lots more fumes per unit volume.
Gasoline engines, the fuel is almost all vaporized before it gets to the combustion chamber

[Wotname]

Igniting diesel isn't rocket science, it is the same as igniting any other liquid (think candle wax or petrol).

The liquid has to be heated until it reaches it vapour point. Then and only then, the vapour will ignite once it reaches it's ignition point.

It is easy to heat a small amount of diesel that has a large surface area with a match but a match does not have enough energy (heat) in it to heat a larger volume of diesel.

Some diesel floating on a large pool of bilge water is much harder to ignite as one has to heat the water as well.

A dry bilge with diesel is more of a concern!!!!!!

[Wotname]

Originally Posted by a64pilot

Even the combustion cause of a Diesel engine is most often misunderstood, it’s not the heat from compression that initiates the ignition in a running Diesel, it’s the heat left in the combustion chamber from the last ignition event, they only “Diesel” when starting.
..........

Pedantic mode ON.

You need enough total heat to start and run a diesel engine. A good percentage of the heat come from the compression, the rest is from the residual heat from the previous ignition and from the incoming air.

Of course when starting there is no residual heat from a previous ignition so all the heat much be obtained from the compression and incoming air unless glow plugs are fitted. In essence, glow plugs supply a heat source to a similar a previous ignition.

Some diesels require glow plugs for starting regardless of ambient air temperature while others don't. This is usually dependant on compression ratio.

However once running, compression still supplies a good amount of the heat required for ongoing ignition. If this wasn't so, a hot engine would continue to run if decompressed.

EDIT: the heat supplied by compression is partly a function of the rate of change of compression - in essence the rpm. When staring the rpm is low so the "compression heat" is low. When running, the heat supplied the compression is much higher as the rpm is much higher. The amount of heat generated is not just given by the compression ratio although clearly at any given rpm, a high compression ratio generate more heat.

Pedantic mode OFF.