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posted to uk.rec.sailing,rec.boats.cruising
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Ted Bell wrote:
If I've read it right a diesel compresses the air to a very great extent. The compression heats the air so much that fuel self-ignites when injected into the hot air. Even if it's very cold it's my understanding the compressed air is still hot enough to ignite the fuel. So it seems to me if the fuel doesn't ignite maybe it's because it's so cold and thick that the injectors don't spray it in properly. It is more common, particularly on engines well past their youth, that compression is not as good as it should be. The result is that the compressed air doesn't get hot enough quickly enough at low revs in a cold engine block. This seems a likelier scenario than the fuel being too viscous at low temperature to disperse properly. Maybe just dribbles of larger droplets that are reluctant to burn. So heating the injectors seems like it would take care of that problem. Sort of the same principle that a pressure diesel stove uses to pre-heat the fuel. Meths don't burn all that hot so although it might blacken the paint I can't see where it would damage the injector. I think I'll give it a go. Many engines are fitted with electric glow-plug preheaters. I don't think they heat the injectors, but part of the combustion chamber. On some engines, electric heater coils are located within the air intake. This is an easy option to retro-fit (unlike glowplugs which really need to be designed in from the start), and Bukh, for instance, offer this option and I can vouch for how well it works. They basically preheat the air, so that it's already warmer before it gets heated by being compressed. The result is that the compression heats the air up to an even higher temperature, making it more likely that the engine will fire sooner. I would recommend that if you want to have a go, it would be a better idea to heat up the air intake than the injectors. |
#2
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posted to uk.rec.sailing,rec.boats.cruising
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Ronald Raygun wrote in
. uk: Many engines are fitted with electric glow-plug preheaters. I don't think they heat the injectors, but part of the combustion chamber. Glow plugs are situated in the path of the spray pattern of the injector, usually in a pre-combustion chamber which not only makes the engine much easier to start, but much quieter to run. http://www.kenrockwell.com/190d/images/lvp.gif Here's the precombustion chamber of a Mercedes Benz 190D diesel. The glowplug is the gold pin right under the spray head. It heats red hot just before the engine starts, causing the fuel to explode reliably as soon as it is injected, by the injector directly above it. It continues to glow, as does the grey resonator under it while the engine is running, not by the electrical current, but by the last time the fuel exploded. The explosion happens in the precombustion chamber and an immense pressure pushes the explosion into the air charge down in the cylinder through those tiny holes, maybe 1/8" diameter, in a radial pattern on top of the piston to balance the pressure on the piston top. After 25 years of constant use, my '73 220D sedan's little 57hp diesel piston had 5 little tracks across the top of the piston showing where the explosion went by it at TDC on ever other stroke. I couldn't get over how small these holes are and how clean they stayed all those years when we overhauled it at about 250,000 miles. It really only needed new rings. Notice in MB cars, the whole chamber screws out so it can be easily replaced if it cracks under the pressure. Smart, very smart. All this is done to reduce the compression necessary to start it cold and run it QUIETLY in a nice car. It ran fine on vegetable oil going to breakfast with my old friends, this very morning...(c; Larry -- Have a little fun in the checkout line.... Ask the nearest American, "Did you see the ICE agents chasing those Mexicans out the back door?" ....Shortens that checkout line right up...(c; |
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