Heat exchangers

A requirement for running your diesel vehicle with vegetable oil with either a single tank, a twin-tank or if running on blend to increase the % of vegoil in the blend. An efficient heat exchanger can make all the difference!! With a good heat exchanger, the engine will not know the difference between vegoil and mineral diesel. Without a heat exchanger the vehicle will be running on a fuel that is 20 times thicker than mineral diesel - It will not burn efficiently and may suffer from all manner of problems ranging from poor fuel consumption and poor emmissions to pump failure and ring gumming (leading to engine failure).

Brazed Plate Heat Exchangers are an extremely efficient means of harnessing the heat from a vehicle's coolant system to heat vegetable based fuels.

These heat exchangers are made up of a stack of rectangular plates which are often made of aluminium or stainless steel. There are narrow alternately connected gaps between each plate. The primary fluid, which is the hot or cold source depending upon the application flows in to the exchanger, through the alternate plate gaps and then back out. Meanwhile, the secondary fluid flows though the exchanger between the plate gaps filled with the primary fluid and is heated or cooled. If sized correctly, the secondary fluid should exit at a temperature almost equal to that of the primary fluid.

These heat exchangers are perfectly suited to heating vegetable oil in vehicles since the primary fluid, the coolant water rapidly flows through the plates delivering plenty of heat, while the fuel flows much more slowly. Since the vegetable oil takes so long to pass through the exchanger, it takes very little heat energy to reach the coolant water temperature which as a result drops very little in the process.

Benefits over hose-on-hose or hose-in-hose systems include reduced loss of heat to ambient and quicker warm up times due to the fact that lengthy runs of coolant lines are not required. Also there is no need to draw on the vehicle's battery power as is required for glow-plug and heater element designs - this is particularly beneficial during the winter months when the battery is under plenty of strain anyhow without the extra demand to heat very cold vegoil. Temperature is regulated and there is no chance of burning the oil as can happen with electric heaters.

Since they are so efficient, the size of plate heat exchanger required is very small, particularly when made of aluminium. Aluminium heat exchangers are made specifically for vehicle applications. BioTuning have a range of heat exchangers to suit all vehicles.

An alternative is the stainless-steel variety as used in combi-boilers . Although most boiler manufacturers use HEs with no hose connectors, some (eg Vaillant) have ones which are suitable. They have BSP screw thread fittings so can be securely connected to the coolant and fuel lines. They are constructed with copper brazing so if you are not keen on using copper then these are not for you. They don't have a fixing plate or mounting holes so a metal strap or other method is required to fix the heat exchanger securely and they are heavy and much larger than the AL types. When bought new they are often more expensive than the aluminium HEs. Second hand, however, these HEs can be picked up very cheaply - even for nothing so if you are on a budget then this could be the HE for you.

Hose-in-hose (HIH), although nowhere near as efficient as the plate heat exchangers, running the fuel line within a length of coolant line, makes a feasible heat exchanger which can be made easily and cheaply. Plans detailing the fabrication of these heat exchangers and listing all of the parts can be found on numerous web sites in many languages. Various materials can be used.

These heat exchangers are often used to run a heated fuel line from the tank to the engine.  There is a risk of the internal hose failing or the connectors leaking resulting in cross-contamination of the fluids and serious problems to the engine.

Hose-on-hose (HOH), these are simply runs or coolant hose running alongside the fuel hose so that the heat from the coolant hose heats the fuel hose. Sometimes the hoses are taped together and put inside the same piece of lagging. Some manufacturers even manufacture a lagged HOH arrangement by the metre. Not efficient at all as a heat exchanger but it is particularly useful in cold climates for heated fuel runs from the tank to the engine. There is not a risk of the internal hose failing resulting in cross-contamination of the fluids 

 Glow plug heaters. These are sold as vegoil fuel heat exchangers. We do not recommend them and certainly would not sell them for the following reasons;

  • Nowhere near as efficient as the plate heat exchangers.
  • Put strain on the battery - particularly in Winter when everything else does
  • Can burn or boil the fuel
  • Require thermostat, relay and switch control. ie not as simple with more failure modes

In our opinion there is simply no need to use electric heating with such a vast amount of heat being generated by the engine. Don't be fooled into thinking you can run on oil instantly if you use a glow plug heater - any heat imparted to the vegoil will be lost the moment the oil touches the injector pump.

How a plate heat exchanger works. Heat is transfered from the coolant in red to the oil in blue. Ripples or baffles between plates increase surface area and induce turbulence to thoroughly heat the oil.

Aluminium heat exchanger. Small, lightweight,  and higly efficient.

Large aluminium heat exchanger. Suitable for vans, trucks, busses etc. Vehicles with high fuel consumption 

Stainless-steel HE from a combi-boiler. It works, but is pretty large and heavy. No mounting plate or bracket so supporting bracket needs to be fabricated to support weight.

While every effort is taken to ensure that the information on this site is accurate we accept no responsibility or liability for any problems encountered while acting upon it.