Here is what I use for preheating vo:
Item #3641k23 page 473 at Mcmaster.
I wrapped the 3ft section of wire around ¼” copper tubing that I used to replace the stock steel line. As you can see from the picture below I added a temp probe using a brass “T” close to the of injection coupling. I was able to get temps as high as 250f and probably could have gone higher if I had not unplugged the heater
That is all fine and good, but I don’t want to baby-sit this thing, so I am going to add a bimetal thermal switch which will be configured as normally closed open on rise at 250f. The switch should arrive by next week.
High pressure line:
I am not sure what kind of pressure the pump creates, and I only used copper because it was easy to work with for this initial test. I had intended on using brake line as the injector line, it has pretty good flex and can withstand higher pressures than the copper. I have tested the copper arrangement for a few weeks and one drawback is the amount of time it takes to purge the system of Veg oil after switching back to diesel. As you can see in the picture below the ID of the copper is much greater than the original steel line, the steel is <2mm and the copper is around 5mm.
The wire above is with the shielding pulled back.
The copper conducts better but the steel is stronger and allows for a quicker changeover, I will use the steel. Another advantage of the steel is that the thickness of the walls allows for some degree of heat storage, it is like a mini heat sink. This becomes important when the load increases, the temp will not drop as quickly as with the thin walled copper. Going along with the heat sink theme the new version I am building will have an area of increased mass to allow for more heat storage. It is in some ways analogous to the flywheel on the lister itself, they store kinetic energy, the increased mass will store the heat, helping to lessen internal veg oil temp swings. See below
That piece of steel is 1 ¼” thick x 1 ¼” wide and about 2” long it weighs about 1lb. The hole in the picture will be taped ¼” NPT to accept the temp switch; there is another hole on the side for the temp probe, which is just an automotive temp gage. The heat rope will be countersunk into the block and the edges will be rounded, I may add conductive putty but I don’t think it will be needed. The entire line and steel piece will be insulated with ceramic insulation from Mcmaster
One last note, it is important to cover the line from the pump on up to the injector, the flywheels create a lot of air movement, simply holding a piece of cardboard under the line allowed the fluid temp to rise at a faster rate.
When the next version is done I will post some pics and some performance data.
Scott