DIY Injector Line Heater

[KenB]

Ivan, List,

The most common cause for poor combustion, poor fuel economy and an excessively sooty exhaust is inadequate heating of the vegetable oil before it enters the injector.

Veg oil is far more viscous than diesel, so you have to get it nice and hot to make it thin and runny.  Anything above about 60C and the veg oil will get thinner and start to inject cleanly with a good spray pattern.  A good mist from the injector means that the bulk of the oil will burn in the power stroke and not come out as half burned soot.

I reckonned that about 100W would be needed to warm the injector high pressure line.  I salvaged a length of 0.5mm nichrome (resistance) wire from an old heater, and made a 25mm long coil of about 10 turns on the hp fuel line. the coil was located about 100mm from the injector, and I alsostrapped on a temperature probe so I could see how the oil was warming up.

The resistance was about 1.5 ohms, so it would draw close to 8 amps at 12V and produce nearly 100W.

The fuel line was first insulated with glass fibre tape, and then rockwool insulation added on top of the coil and the remainder of the injector line.

The technique was successful, soon the injector line and the oil inside it was up to greater than 70 degrees C.  Tomorrow I will do some fuel efficiency and smoke tests to see if the hot injector line is really helping.

Here's a couple of pictures.  The first shows the position of the coil on the hp line but insulated with a scrap of rockwool. The second, rather blurry picture shows the coil glowing orange hot and transferring useful heat into the fuel oil.

Best or neater solution would probably be one of those PTC thermistor type heaters, these run on 12V-24V dc or 100V to 240V ac. They self regulate and heat up to a fixed temperature (40 to 200C)and with variable wattage 20W to 200W. Priced about £12  each for the higher power devices from Farnell. 100W regulating to 120 C should be enough to cook the oil nicely.
 
Alternatively  thick film 100W power resistors are available in a TO247 plastic package. Two could be bolted back to back with the hp line between them.  About £4.5 each from Farnell.    Remember to insulate well -the heat needs to get into the oil not be dissipated in the air.



Ken

[Ivan]

wow! That looks hot!

I have seen pipe-in-pipe water heaters used on cars - you could place 8mm tube carrying fuel inside 10mm pipe. With a bit of modification, you could use two solder fittings 8mm/10mm adaptors at either end with some 10mm T-s to give you the side connections for water. As usual, I am ashamed to admit the lack of experimental effort.


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[KenB]

Ivan, List,

I was planning to build a low pressure heat exchanger from plumbing fittings as per your sketch, and fit it just before the injector pump.

If the oil enters the pump hot, it will be warm on exit, and so the high pressure line heater will bring it up to an even greater temperature.

I believe that expending 100W of electrical power on a hp line heater, will more than pay for itself in easier starting, better fuel efficiency and reduced smoke.

I had an idea for the high pressure  line heater using a diesel glowplug set into a steel block and fitted with male and female diesel unions. It would have to be steel, as copper and aluminium will not survive the pressure on this side of the pump.

There are T pieces available for hydraulics,  that are rated at 120C, there is a part called a "swivel nut run tee"   which has a male entry and a female exit and a male thread on the side T.  This could be screwed onto the injector union and the diesel glowplug set in via the side T so that it directly heated the oil.

RS stock these, as will most hydraulic specialists. I just have to confirm what pipe thread they use on the injector and hp line, and what thread the diesel glowplug uses.  I think it's 3/8 BSP but need to confirm.
 


Ken

[billi]

hello  ken

i am sure you know about heating the oil via a waterheatexchanger from the radiator

that worked very good with my diesel truck, just the coldstarting was a bit heavy in winter ,  here is a combi heatexchanger  that preheats with two glowplugs at 12 v 340 watt and stops after cooling temp is high enough to handle the rest of the running time

the coolant liquid goes through the same unit

all the best lars

[KenB]

Lars,

Thanks for that - I was already aware of these heater units for the low pressure side of the pump.

My heater is specifically to heat the oil right before it goes into the injector.  100W of heat here can make a big difference to the overall efficiency of the engine, easier starting and reduction of soot.




Ken

[Twenty4Seven]

Hi Ken

Have you considered one of these glow plug COV replacements......



http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=190167956155&ssPageName=STRK:MEWA:IT&ih=009

After several unsucessful bids, I won the last one for under a tenner....

Cheers

Nick

[KenB]

Nick, List

Yes, thanks for that,  I have one of those too, but haven't installed it yet.  I've been busy doing carpentry this week.

My understanding is that the heated oil will inject with a better spray pattern and burn more easily with less carbon build up.

I think I am correct in my hypothesis that heating the injector line is the most efficient way of achieving better overall running - though yet to be proven of course ;-).

Engine shed just grew another 8 feet.  My cat is now looking worried because there's now plenty room to swing him.    I now have a quieter test area for the dynamometer control unit, and the all important kitchen sink - soon to have hot running water - ideal for washing WVO from hands.

Digital camera still hasn't sorted itself out - might have to drop a bit of 4 x 2 on it again, or treat myself to a new one.


Ken