The road to pure plant oil in diesel engines?

Using rapeseed oil in vehicles

This chapter discusses using PPO in combustion engines. This is followed by a look at the techniques used, users’ experiences, air pollution emissions and the related health aspects, plus the costs of using PPO in vehicles. The chapter closes with a number of points that need further consideration plus a number of improvement prospects.

Technology

Engines need to be modified before they can run on PPO. This is due to the higher viscosity and molecule weight, lower cetane number and the higher flashpoint of the fuel, whereby ignition is more difficult. These are also the most important differences with ordinary (fossil) diesel.
The viscosity of PPO (particularly at low temperatures) is much higher than that of traditional diesel fuel (see Figure 7.1). Before PPO can combust correctly in a diesel engine, the fuel must first be heated to around 60ºC. In some cases the injection time needs to be modified and special injectors or atomisers need to be fitted to the engine. This depends on the type of vehicle and the converter. Since PPO is pH-neutral, pipes and gaskets do not need to be replaced.

Viscosity of fossil diesel, compared to rapeseed oil

The available conversion technologies are also still in development. Converting from older indirectly injected diesel engines and the newer direct-injected diesel engines using the Bosch atomiser system with a central injection pump, is the most-used technique. However, for direct-injection systems such as common rail engines and systems with multiple injection pumps, there are still very few conversion packs available, and these are still being developed. It also seems as if every vehicle will need a different conversion pack, and sets have only been developed for a limited number of vehicle types, i.e. Audi, Ford and Volkswagen. PPO could thus, at the moment, only be used for a limited number of vehicles during large-scale introduction.
Up to now, the development of conversion packs has taken place in small companies that do not have good connections to the large engine manufacturers. In Germany, the conversion itself is only carried out at a few garages and small companies. In other words, it is not current technology and know-how, and (due to the limited manpower) it is debatable how fast this know-how development can occur. In addition, the size and structure of the current ‘conversion industry’ raises questions as to how fast this industry could supply the required conversion packs necessary for large-scale implementation of PPO as a vehicle fuel.
There are two modification systems available: a single-tank system and a two-tank system.

Single-tank system

With a single-tank system, both PPO and diesel can be used in the tank. A vehicle with a single-tank system should be fitted with a pre-heating system, to improve the viscosity of the fuel in cold weather. The single-tank system can only be used for a limited number of cars (of which the management source codes are known), because the engine management systems need to be modified. These are generally only known to the car manufacturer, so this system is only used to a limited extent.

Two-tank system

With a two-tank system, the vehicle starts up using ordinary diesel, and the PPO is heated to around 60°C via a separate fuel flow system. Once the PPO is up to temperature) after around 15 minutes, a small onboard computer switches the engine over to PPO. This system is fully automatic, with a small display on the dashboard. Towards the end of the journey the driver switches back to diesel, to ensure that there is no PPO left in the fuel lines and to prevent startup problems and blockages in the pipes and filters. This system uses ordinary fossil diesel when starting and stopping the vehicle.
When converting a standard vehicle, modified atomisers are generally used, and a heat exchanger, thicker fuel lines and a fuel filter (1Sm) are added. A number of electronic adjustments are also made.
The two-tank system is currently preferred because this has been tested for the Dutch climate. However, it is more expensive than the single tank system.

Converting cars with the 1-tank system

With this system, there is no additional tank; all the fuel is held on the original tank of the vehicle. This solution relies on the adaptation of the injection process to the injection characteristics of vegetable oil, so typically, the glow-plugs, injectors, and injector mounts are modified.
With this system, you can drive entirely without diesel, except in the winter months, when a certain amount of winterdiesel should be added to the vegetable oil in the tank to keep it flowing freely.
As with the 2-tank system, you can still run on straight diesel, or in any mix of diesel and vegetable oil.

The 1-tank system can be fitted on pre-chamber diesels of most makes, as well as on traditional TDI engines from the Volkswagen group (AUDI, SEAT, Skoda, Volkswagen and some Ford and VOLVO as well as 1.9 dTi motors from Renault)

The typical 1-tank conversion kit would contain the following parts:
§ injector components
§ glow-plugs
§ additional fuel filter
§ sometimes additional fuel pump
§ coolant-water heat exchanger to pre-warm fuel
§ electrical fuel heater/filter
§ temperature switch
§ cut-off valve
§ Relays and sockets
§ fuel and water pipes
§ fuel hand pump
§ cabling

If an auxiliary heating system or night-heater is desired, then a small secondary tank should be fitted for diesel, as these heaters do not run on vegetable oil.

Converting cars with the 2-tank system

The 2-tank system has a separate diesel tank to start and warm up the engine. Once the engine is warm, it switches over, automatically or manually, to take vegetable oil from the main tank of the vehicle for the main part of the journey. Before long stops where the engine might cool down, the driver switches back to diesel for the last few kilometers of the journey. This flushes the vegetable oil out of the injection system ready for the next cold-start.

The auxiliary tank for a car typically has a capacity of 20-30 litres. In some countries it must be noted in the vehicle particulars by a testing centre, and may be required to have a filler pipe on the outside of the vehicle.

The typical 2-tank conversion kit for a car would contain the following parts:
§ small auxiliary fuel tank
§ in some cases glow-plugs
§ additional fuel filter
§ electrical fuel pumps
§ coolant-water heat exchanger to pre-warm fuel
§ temperature switch
§ changeover switch
§ Relays and sockets
§ fuel and water pipes
§ cabling

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