Tuesday 26 June 2007

Changes to the fuel diagram

Click the images to enlarge them :)

I've finally drawn a decent fuel circuit diagram for the 300D.


For a larger pdf file version, click this link 

Changes made to the original setup are:

1. Added a glow plug heater just before the injection pump (IP). This modification allows me to change over to veg after only a couple of minutes from start-up. Ideally, we need to try to achieve a temperature of 90degC at the IP. At this temperature most veg oils will have a viscosity that approximates dino-diesel, for which all modern IPs are designed.

My home made glow plug heater is made from commonly available plumbing parts and uses a single 14V pencil-type glow plug. It's installed in between the lift pump and the IP and is controlled by a 100degC thermo-switch, so it is constantly cycling on and off. A fused relay ensures that if the thermo-switch fails the GP will not "run-away"and burn unchecked. In actual fact, I thought it was a 24V volt GP as that is what I asked for, but have since noticed that 14V is etched onto it????!!! Previously I was blowing the 12V variety quite regularly (11V etched on that GP). Anyway, this single 24V/14V (whatever) plug has worked flawlessly for the past 10 months and does an excellent job at heating the oil very quickly.

I think the secret is to use a nice lump of brass for these GP heaters. They heat the oil that passes though instantly, but as soon as the fitting gets to your selected temperature, the housing does most of the heating and the GP doesn't have to work as hard, so cycles off and on less often. Also, it retains a lot of it's heat if you have stopped for 1/2 hour or so. It will do an even better job if you take the time to insulate it.

You will see that I've used a "3-port"plumbing fitting. Suitable reducers were found to match the threads of the GP and the hose fittings. The GP can be installed in any of the "ports". I chose this configuration to suit my layout and to facilitate needing to change the GP easily.

I added some thermal grease to facilitate better heat conductivity from the brass body to the thermo-switch.

BTW, I am getting this reliability from a $10 GP off eBay!

Tips:

  • Strip the paint off the GP before installing it or you run the risk of the paint entering your fuel line.
  • Ensure that you prime the fuel lines properly. Air in the fuel line might cause premature failure of the GP or "charring"of the fuel.
  • Install an in-line filter between the GP heater and the IP as insurance just in case the GP fails and fragments, or to catch any charred bits. Better the bits in the filter than in the IP :)
  • You could also install another heat exchanger in place of the GP heater. This will work very well, but it will not have the advantage of the GP heater that will heat the oil to allows quicker changeovers.
  • As further insurance, you do have a serviceable fire extinguisher in your car don't you? They come standard in all Mercedes models and are essential equipment in any vehicle.

2. The other modification of the original installation was to send the IP overflow and IP returned fuel back to the veg tank. Previously this was looped back into the fuel circuit just before the heat exchanger. This task is managed by the 6-port Pollak fuel selector valve which has performed flawlessly. The returned fuel is still quite warm and sending it back to the veg tank warms the fuel and has cured the problem mentioned in my previous post where the high melting point (HMP) fats were clogging the fuel line fittings on the marine tanks. The relatively small size of the tanks (25litres) means that they warm up quite readily. I carry two of these tanks at all times, with the second one ready to be connected when the other runs dry.

I also added a small Facet lift pump and an in-line filter before the flat plate heat exchanger. See diagram.

In my next post, I'll upload a diagram that shows how to wire the glow plug heater.

14 comments:

Anonymous said...

Hello,
I'm trying to figure out how make injection line heaters instead of buying more fattywagon ones. I want to wrap the injection lines on a 6.5 chevy. Can you email me?

Thanks
jon krouse
jonkrouse@comcast.net

oztayls said...

Hi Jon

I presume you have a single tank system then and you need the lines heated in order to start the engine? If you have a two-tank system, you don't need these line heaters.

I have not made these lines myself, as I heat my system from coolant and a single glow plug heater, but they would be simple enough to make.

An electronics store eg. Jaycar will have what you need. You need to wrap the lines with an electrical insulator before winding the correct length of resistance wire (heater wire) around the line, and finishing off with silicon self-amalgamating tape. There are calculators on the web to help you calculate the length of resistance wire you would need to achieve the output you require. You could use a similar relay and thermoswitch to the one on my blog that controls the glowplug heater.

Cheers
Bruce

Unknown said...

Gday Bruce,

This might sounds stupid, but how does having a fuse on your glow plug heater stop it from burning out if the thermo switch stops working? My only thought is that as the GP gets hotter and hotter, the resistance drops, thus draws more current blowing the fuse.. But does resistance change that much? If so, how did you size your fuse to the GP? I'm asking as I am making one of these myself, but don't want to start an engine bay fire with super hot vege oil..!

Thanks
Sam

oztayls said...

Good question Sam. You will need to use a thermostat switch that is normally closed. This is wired from a power source when the ignition is on only as you don't want it working when the ignition is turned off! Using a thermostat switch that is normally closed means that it starts heating straight away, and goes open circuit when it reaches temp, for eg 100degC. If the thermo switch fails it will go open and turn off the GP. Just in case things go wrong though I recommend you instal a thermal fuse that will blow at around 132degC.

Unknown said...

Ah, of course, thanks. As you say, of course, if it's a NC switch, failure will mean that it becomes NO, which of course means you have nothing to worry about in terms of overheating.
Thanks for your blog, great help to us DIYers.
How has your GP gone lately? Have you had to replace since switching to 24v? Imagine it will last a very long time if it's 24v, as only drawing half the current it's rated to on a 12v system.
One last question.. Have you had any problems with those thermo switches durability? I imagine they're not made for getting wet & outdoor purposes, does it handle it ok?

Cheers
Sam

oztayls said...

Sam, I'm still using the same 24V glow plug. Also the $4 thermoswitch has proved to be totally reliable :) I had a couple of fuel leaks from my GP heater. I was using plumbers tape to seal it, but pulled it apart and instead used a thread sealant (Loctite) and have had no problems since.

Unknown said...

Thanks Jon,

I've bought all my gear and will be trialling it soon, I'll let you know how it goes.. I'm also going to pull apart one of those bi-metallic relays to see how well sealed they are, will let you know results.

Yep locktite seals nicely, although watch when pulling GP heater apart again in future that solid bits of locktite don't end up in fuel line! Although I see from your schematic you have a filter post-GP heater, so prob nothing to worry about!

I have a 12v GP at moment, but having difficulty finding a small (as in dimensions) 24v GP such as yours. Any chance you would let me in on what brand/model number yours is?!..

Sam

oztayls said...

Hi Sam, not sure why you're so worried about the thermoswitch. They are very reliable and used in lots of applications.

Yes, the reason for post GP heater filter is to catch any crap or carbon that might break loose from the GP. So far the GP has not shown any build-up of carbon though, but methinks it is still a good idea to have that cheap disposable filter there. If you need to change GPs, it would probably be best to remove the whole heater anyway to give it a clean and checkup before reinstalling the new GP.

The 24V GP is a AU$10 cheapie off evilBay. It is longer than the one shown in the pic but I installed it on the end instead. Doesn't really matter, as long as the fuel passes over the heated tip.

Anonymous said...

I found a bunch of 6v glow plugs at my local part house they were trying to get rid of. do you know the amperage of your glowplug? I'm estimating about 20 amp to figure out the type of resistor i need.

oztayls said...

G'day Caw42883, At the time I purchased them, I was told they draw about 20-30amps initially and then taper of to about 15amps. However I have never measured the current draw as I have never experienced any battery problems with the 24V GP.

Please consider the level of complexity you're introducing and when designing your set-up, what the repercussions are if one plug fails :)

Anonymous said...

Right now I'm thinking of getting a 85 amp alternator, a 40 amp relay, and a 70C normal open switch connected to a led to indicate temp problems.

Feel free to e-mail me, I would love to bounce my system ideas against you.

colby.westerfield at gmail.com

oztayls said...

G'day Caw42883

An 85amp alternator is nice if you have a big current draw, but in this instance I think it's overkill unless you can get one real cheap.

Have you checked eBay for a cheapish 24V GP?

You will need a "normally closed" thermoswitch and I would go with 90
or 100degC so as to achieve 70-80deg at the IP. You need a normally closed switch so that when you reach the designated temp, the bi-metallic element goes open circuit, and switches off the GP. The unit resets automatically when temperature falls the below specified limit, which on the 90-100deg switches is about 70-80deg.

The other method to skin this cat is to install another HE before the lift pump or IP in lieu of the GP heater. You could have a valve so that if you were running dinodiesel for a while, you can bypass the HE.

Cheers
Bruce

Jason said...

I am asking as making one of these myself, but don't want to start an engine bay fire with super hot vegetable oil!

oztayls said...

What are you asking Jason?

I'll take a guess that you're concerned about the potential temperature generated by the glow plug and it will cause the oil to ignite? The 90-100degC thermo-switch prevents the oil from being heated to temps above the intended range.

The first question to ask is whether you really do need to install a GP heater in the first place. It is really only of use in cases where the change-over from diesel fuel to veg is slow.

It has been a few years now since I did all this. While the GP heater worked well, I have since decided it was a complication to the overall design that really isn't necessary, so the GP heater was removed.

By all means, if you trust your workmanship to make a GP heater that won't leak, go ahead and make one. It works! However, I eventually decided to remove mine as the overall benefits were small due to the fast changeover from diesel to veg fuel that this circuit design achieves.