Some questions on ambulance powerplants:

[Richard B the EMT]

On a separate string, there is a discussion on the (alleged) virtues of diesel versus gasoline power plants in ambulances, as Ford is reintroducing gas powered V-10(?) engines for the 2010 model year.

This might be better answered by personnel who have more than the basic Hazardous Materials Awareness level of training, which is where I currently am at. I admit to not really knowing much about any car/truck engine repair, but presume I am not the only one with that particular educational lacking.

Someone on the string mentioned that, in a potentially explosive atmosphere, it was under a federal mandate (in the United States), that Emergency Response vehicles should be diesel powered, as there is danger of the spark plugs and/or electrical system of a gasoline powered vehicle igniting explosive fumes.

1) Could someone give both quote and link to this mandate?

2) Could a plume of a potentially explosive vapor be triggered into an explosion by some random spark inside a gas fueled engine?

3) Could such vapor plume cause an explosion by being sucked into the air intake of a gasoline powered engine, and "flash back" through the air intake from the spark plug inside the engine?

4) As diesel engines use a non sparking gizmo called, I think, a "glow plug", referring back to question 3, could the diesel engine cause an explosion via the air intake, as previously described?

4-A) If it isn't called a "glow plug", could somebody tell me the real name, and how diesel engines generally work?

As always, in questions like this, asked by your humble servant (yeah, riiiight! the man, the myth, the legend in his own mind, HUMBLE?), I thank, in advance, any and all who respond with legitimate answers to these questions.

[rock_shoes]

In reference to a diesel engine "Glow Plugs" are a starting aid only. Once the engine is running combustion is solely due to heat and compression. Not all diesel engines use glow plugs. Some use an intake grid heater instead (the 5.9 and 6.7 litre cummins engines for example) while others use a combination of the two (later versions of the 6.6 litre duramax).

The benefits to using a diesel engine (in an ambulance) outweigh the negatives in a number of ways (In my opinion of course). First off diesel engines are inherently 20-40% more fuel efficient than similair sized gas engines. The service life of a diesel is significantly longer than that of a gas engine and the torque curve associated with diesel power is far better suited to moving large loads efficiently. There is a reason heavy industry uses diesel technology almost exclusively.

Negatives, though not inconsequential, are fewer than the positives. Initial outlay for a diesel engine is significant and a diesel engine is heavier. The weight issue isn't nearly the problem people think it is when a vehicle is already as heavy as an ambulance. In addition to that their are a number of new technologies well on the way reducing that weight penalty (Compacted Graphite Iron). As for performance and power diesel has become the "more power" option. A new Duramax pick-up for example puts out 365HP, apprx. 650lbFt of torque, and lower overall emissions than a big block gas. If you still doubt the performance potential of a diesel engine keep the multiple Le Mans winning Audi R10 TDI in mind.

North Americans as a whole have turned their collective noses up at diesel for far too long. Everyone thinks of the failed Oldsmobile 350 diesel beltching black smoke in the late 70's and early 80's. Overall european car sales are apprx. 50% diesel primarily for fuel efficiency reasons.

[reaper]

On a separate string, there is a discussion on the (alleged) virtues of diesel versus gasoline power plants in ambulances, as Ford is reintroducing gas powered V-10(?) engines for the 2010 model year.

This might be better answered by personnel who have more than the basic Hazardous Materials Awareness level of training, which is where I currently am at. I admit to not really knowing much about any car/truck engine repair, but presume I am not the only one with that particular educational lacking.

Someone on the string mentioned that, in a potentially explosive atmosphere, it was under a federal mandate (in the United States), that Emergency Response vehicles should be diesel powered, as there is danger of the spark plugs and/or electrical system of a gasoline powered vehicle igniting explosive fumes.

1) Could someone give both quote and link to this mandate? I have never heard of any mandate like this. Most use diesels now, due to longevity issues.

2) Could a plume of a potentially explosive vapor be triggered into an explosion by some random spark inside a gas fueled engine? Not really. A spark from something else can set it off.

3) Could such vapor plume cause an explosion by being sucked into the air intake of a gasoline powered engine, and "flash back" through the air intake from the spark plug inside the engine? In easy terms "no it can not" Once the intake valve closes, the combustion chamber is sealed. All spark and combustion is trapped in the cylinder, until the exhaust valve opens. to let it out.

4) As diesel engines use a non sparking gizmo called, I think, a "glow plug", referring back to question 3, could the diesel engine cause an explosion via the air intake, as previously described? Same concept as above. Diesels use no open spark.

4-A) If it isn't called a "glow plug", could somebody tell me the real name, and how diesel engines generally work? Yes, it is called a glow plug. Diesel fuel ignites from heat and pressure, not spark. A glow plug is only used on initial start up, to warm up the combustion chamber. Once the combustion process heats the chamber, it will continue to ignite the following combustion sequences.

As always, in questions like this, asked by your humble servant (yeah, riiiight! the man, the myth, the legend in his own mind, HUMBLE?), I thank, in advance, any and all who respond with legitimate answers to these questions.

These are simple answers to your questions. You can google diesel combustion process, if you want a more in depth read on the subject.

[CBEMT]

Why is the ambulance close enough to a Hazmat scene to ignite vapors that are highly concentrated enough to ignite?

[a_shane2_go]

Early on in my career I worked in the oil patch and received some basic safety training, and our MTC's (Mobile Treatment Centers) and once in a while a 4x4 ambulance would be on a rig site with the potential for release of hydrocarbons, H2S and other hazardous materials. (Acids, etc.)

Both diesels (99% of light+heavy trucks used when I was working) and half the trucks i was working in had a shut off switch for the intake of the engine. (So that if there was a release, the truck would not in theory cause a spark to open air causing it to go BOOM.)

And once I tested out how far it would go after pushing the button, probably 3 or 4km before the engine crapped out. (And I learned I had to disengage it by throwing the hood up and manually placing the closing mechanism near the throttle body to the open position.) lol

Anyways I don’t see a problem with gas engines for ambulance. Because if we are in a potential environment for ignition, both have the potential to ignite and we are in way over our head unless we are dual trained in HAZMAT (or fire?)

These were also sites who had a dedicated gas analyzer on staff and intrinsic radio's which most ambulances don’t carry as they can "technically" have a potential to spark. (Again fire may carry these) but most private operators wont dish out the extra money when they are not generally needed for EMS side of things.

I am far from a mechanic (I do all my own maintenance on my truck) and this is only from my personal experience, hope I provided some insight

[TDP]

In regards to older diesel engines in the way of operation fuel and air is mixed in a pre combustion chamber before it was injected into the cylinder. all of the mixing and injections are mechanically,not electronic or direct inject. a good example is the first gen 5.9L cummins 12 valve And for the new engines everything is pretty much computer control/injected.

and the rest i stole from wiki, read here

Starting

In cold weather high speed diesel engines, which are mostly prechambered, can be difficult to start because the mass of the cylinder block and cylinder head absorb the heat of compression, preventing ignition because of the higher surface to volume ratio. Prechambered engines therefore make use of small electric heaters inside the prechambers called glow plugs. These engines also generally have a higher compression ratio of 1:19 to 1:21. Low speed and compressed air started larger and intermediate speed diesels do not have glowplugs and compression ratios are around 1:16. Some engines use resistive grid heaters in the intake manifold to warm the inlet air until the engine reaches operating temperature. Engine block heaters (electric resistive heaters in the engine block) connected to the utility grid are often used when an engine is turned off for extended periods (more than an hour) in cold weather to reduce startup time and engine wear. In the past, a wider variety of cold-start methods were used. Some engines, such as Detroit Diesel engines and Lister-Petter engines, used a system to introduce small amounts of ether into the inlet manifold to start combustion. Saab marine engines, Field Marshall tractors (among others) used slow-burning solid-fuel 'cigarettes' which were fitted into the cylinder head as a primitive glow plug. Lucas developed the 'Thermostart', where an electrical heating element was combined with a small fuel valve. Diesel fuel slowly dripped from the valve onto the hot element and ignited. The flame heated the inlet manifold and when the engine was turned over the flame was drawn into the combustion chamber to start combustion. International Harvester developed a WD-40 tractor in the 1930s that had a 7-liter 4-cylinder engine which ran as a diesel, but was started as a gasoline engine. The cylinder head had valves which opened for a portion of the compression stroke to reduce the effective compression ratio, and a magneto produced the spark. An automatic ratchet system automatically disengaged the ignition system and closed the valves once the engine had run for 30 seconds. The operator then switched off the gasoline fuel system and opened the throttle on the diesel injection system. Recently direct-injection systems advanced to the extent that prechambers systems were not needed using a common rail with electronic fuel injection.

[edit] Gelling

Diesel fuel is also prone to "waxing" or "gelling" in cold weather, terms for the solidification of diesel oil into a partially crystalline state. The crystals build up in the fuel line (especially in fuel filters), eventually starving the engine of fuel and causing it to stop running. Low-output electric heaters in fuel tanks and around fuel lines are used to solve this problem. Also, most engines have a "spill return" system, by which any excess fuel from the injector pump and injectors is returned to the fuel tank. Once the engine has warmed, returning warm fuel prevents waxing in the tank. Due to improvements in fuel technology, with additives waxing rarely occurs in all but the coldest weather when a mix of diesel and kerosene should be used to run a vehicle.

[edit] Fuel delivery

A vital component of all diesel engines is a mechanical or electronic governor which regulates the idling speed and maximum speed of the engine by controlling the rate of fuel delivery. Unlike Otto-cycle engines, incoming air is not throttled and a diesel engine without a governor can not have a stable idling speed and can easily overspeed, resulting in its destruction. Mechanically governed fuel injection systems are driven by the engine's gear train. [12] These systems use a combination of springs and weights to control fuel delivery relative to both load and speed. [12] Modern, electronically controlled diesel engines control fuel delivery by use of an electronic control module (ECM) or electronic control unit (ECU). The ECM/ECU receives an engine speed signal, as well as other operating parameters such as intake manifold pressure and fuel temperature, from a sensor and controls the amount of fuel and start of injection timing through actuators to maximize power and efficiency and minimize emissions. Controlling the timing of the start of injection of fuel into the cylinder is a key to minimizing emissions, and maximizing fuel economy (efficiency), of the engine. The timing is measured in degrees of crank angle of the piston before top dead center. For example, if the ECM/ECU initiates fuel injection when the piston is 10 degrees before TDC, the start of injection, or timing, is said to be 10° BTDC. Optimal timing will depend on the engine design as well as its speed and load. Advancing the start of injection (injecting before the piston reaches TDC) results in higher in-cylinder pressure and temperature, and higher efficiency, but also results in elevated engine noise and increased oxides of nitrogen (NOx) emissions due to higher combustion temperatures. Delaying start of injection causes incomplete combustion, reduced fuel efficiency and an increase in exhaust smoke, containing a considerable amount of particulate matter and unburned hydrocarbons .

[edit] Major advantages

Diesel engines have several advantages over other internal combustion engines.

* They burn less fuel than a gasoline engine performing the same work, due to the engine's high efficiency and diesel fuel's higher energy density than gasoline..[1]

* They have no high-tension electrical ignition system to attend to, resulting in high reliability and easy adaptation to damp environments.

* They can deliver much more of their rated power on a continuous basis than a gasoline engine.

* The life of a diesel engine is generally about twice as long as that of a gasoline engine [13] due to the increased strength of parts used, also because diesel fuel has better lubrication properties than gasoline.

* Diesel fuel is considered safer than gasoline in many applications. Although diesel fuel will burn in open air using a wick, it will not explode and does not release a large amount of flammable vapour.

* For any given partial load the fuel efficiency (kg burned per kWh produced) of a diesel engine remains nearly constant, as opposed to gasoline and turbine engines which use proportionally more fuel with partial power outputs. [14][15][16][17]

* They generate less waste heat (btu) in cooling and exhaust.[1]

* With a diesel, boost pressure is essentially unlimited.

* The carbon monoxide content of the exhaust is minimal, therefore diesel engines are used in underground mines.[18]

Besides,why are you parking close to a hazmat scene?curious

[rock_shoes]

Why is the ambulance close enough to a Hazmat scene to ignite vapors that are highly concentrated enough to ignite?

Excellent question. Silly medic. Hazmats are for fire-men.

[Dale]

1) Early diesel engines from GM were simply a converted gasoline model and they suffered from poor performance.

2) Gasoline engines have improved designed and now use fuel injection instead of carburators for much better performance, less heat, etc.

3) Gasoline engines are built to be lighter in weight than comparable diesel engines. On many ambulance chassis such as E-series, reducing the front end "dead" weight of 600-800# by using a gasoline engine versus a diesel version means less potential from overloading the rated front axle weight limit, which is a big problem for many organizations not to mention a violation of Federal Motor Vehicle Safety Standards (FMVSS.)

I know of several agencies that have switched to gasoline engine chassis from diesel. Some of this is the initial cost savings in the chassis purchase price, better fuel economy in the new design gasoline engine, and the reduced purchase price for gasoline versus diesel fuel.

4) Contrary to rumor, diesel engines are not "mandated" by Federal law for ambulances. After a series of ambulance fires in the 1980's, primarily with Ford-chassis ambulances, Ford established the QVM (Quality Vehicle Modifier) program for body builders to address good engineering practices, which were determined to be lacking in many vocational body builder types such as ambulances, school buses, RVs, etc. At the same time, Ford "mandated" that diesel engine chassis would only be allowed for use as ambulances to reduce the problems they were having at the time with gasoline engine chassis (fires, fuel spillage and overflow, etc.) Now, for 2010 Model Year, Ford will once again be introducing a new Gasoline engine for optional selection for ambulance chassis use.

[Richard B the EMT]

...

I know of several agencies that have switched to gasoline engine chassis from diesel.

...

After a series of ambulance fires in the 1980's, primarily with Ford-chassis ambulances, Ford established the QVM (Quality Vehicle Modifier) program for body builders to address good engineering practices, which were determined to be lacking in many vocational body builder types such as ambulances, school buses, RVs, etc. At the same time, Ford "mandated" that diesel engine chassis would only be allowed for use as ambulances to reduce the problems they were having at the time with gasoline engine chassis (fires, fuel spillage and overflow, etc.)

OK, you just reminded me. the NYC Health and Hospitals Corporation EMS had a converted bus they set up as a mobile command center/field comm unit. Due to the time the EMS was all gasoline powered, they converted an intercity/interstate bus frame from diesel to gasoline. The vehicle was horrid due to that. Every time they used it, either for drills or actual Multiple Casualty Incidents, something went wrong with the damn thing. Fastest example was, for a vehicle that actually was rarely used, why did it lose it's muffler each time it went out? I have no answer to that one.

EMS eventually gave the thing to the Mayor's Office of Emergency Management (OEM), and stored it down the street at the NYPD's Central Repair Service garage.

As for the ambulance fires, correct, they were due to horrible design conversions. Placing a relocated fuel line over the exhaust pipe? Putting the radiator overflow recovery tank so close to the engine block that it would melt, and engine coolant (which contains alcohol, which is a fuel) would fall onto the engine and ignite?

Yup, the ambulance builders did that.

Ford's QVM addressed the problems, and, as far as I know (subject to information others have that I don't, YET), other chassis/drive train makers followed suit.