The diesel engine

Dr Rudolf DieselThis page provides some basic information about diesel engines relevant to their conversion to running on straight vegetable oil (SVO). It also includes details on how to find and identify fuel injector pumps.

There are now at least four types of widely used diesel engines; these are distinguished by the way the fuel injection system works. The four types are described here:

Indirect injection (IDI)

In these engines fuel is not injected directly into the top of the cylinder, it is sprayed indirectly via a combustion chamber or swirl chamber which adjoins the top of cylinder; hence the name indirect injection. It is in this pre chamber that the majority of fuel combustion takes place. The fuel injection pump used on these engines times a single injection of fuel into each combustion chamber in turn. This timed injection is synchronised via the timing belt or chain of the vehicle. Two kinds of fuel injection pump are commonly used with this type of engine: rotary or inline pumps. These two types can be distinguished by the location of the injection pipe outlets on the pump. With rotary pumps the outlets are arranged in a square, or circular configuration at the side of the pump. Where as on an inline pump the outlets tend to be in a line on the top of the pump. Engines of the indirect design are in fact the best for converting to run on SVO provided they have suitable pumps, and because of this many can be fitted with Elsbett one tank conversions.

Direct injection (DI)

In these engines the fuel is injected directly into the cylinder where the combustion takes place. This increases the amount of energy from the combustion converted to motion making vehicles with these engines more efficient than the above. Direct injection engines can use similar injector pumps to those used in the IDI systems giving timed single injections of fuel to each cylinder in turn synchronised by a timing belt. Certain types of these engines which have not progressed on to common-rail direct injection or unit injection can be converted with an Elsbett one tank system.

Common-rail direct injection (CDI)

In these types of diesel engines fuel is also injected directly in to the cylinders of the engine, however the fuel injection pumping system is different to the above. With common rail direct injection the main fuel pump does not pump to each cylinder in turn. Instead it pumps fuel at pressure into a “common rail” which is a common pipe, resilient to high fuel pressures which branches off to each injector. Computer operated valves then control when the fuel injection into the cylinder occurs rather than the timing of the pump. This allows the pressure at which the fuel is injected into the cylinders to be increased, which creates a better combustion of the fuel. Better combustion leads to better fuel efficiency and also lower unburnt or partially burnt emissions. Some manufacturers refer to this type of engine as high-pressure direct injection (HDI). These systems currently can only be converted with two tank conversion systems as they have to start up on diesel. The two tank kits are also not of the conventional type as additional pumps need to be fitted to these systems.

Unit Injection (UI)

This is the injection system design used on the most modern diesel vehicles although the idea has been around for some time. Fuel again is directly injected into the cylinder of the engine. However in this system the injector, which injects the fuel into the cylinder and the pump which creates the necessary pressure to allow this are combined into one unit. Therefore each cylinder has its own pump. In Volkswagen – Audi engines they call this system Pumpe-Düse which translated means pump injector. Currently these engines cannot be converted with an Elsbett one tank system and like the CDI engines require special two tank conversion systems.

Locating a fuel injector pump

This is a beginners guide to locating your fuel injector pump. It intended for vehicle owners who have IDI engines or DI engines which do not fall into the CDI or UI category.

Often the first thing that needs to be done before it is possible to get a good view of the engine is to remove the engine cover, if one is fitted. This can often be unbolted quite easily. Once you can get a good view of the engine it should be possible to see a row of injectors with various pipes attached to them running along the length of the upper part of the engine. These are often in a similar location to where the spark plugs would be on a petrol engine. The pipes that go in to the very ends of the injectors are the injector supply pipes and these can be followed back to find the fuel injector pump. If the fuel injection pump is rotary in design then the injector pipes will come out in a square or circular group from the side of the pump. If engine has an inline pump then the injector pipes will come out of the pump in a row across the top of it. The location of the fuel injector pump on an IDI Peugeot/Citroen engine can be seen here. The fuel injector pump is not always located in such a convenient position at the front of the engine for viewing. On Vauxhall Corsa diesel engines the pump is hidden on the opposite side of the engine. In such cases a mounted mirror is often needed to increase the ease with which the pump can be examined.

Fuel pump identification

Here are some pointers in distinguishing Bosch and CAV/Lucas pumps. These are often the two types of pump that need to be differentiated on European manufactured cars.

The standard Bosch rotary pump for a four cylinder indirect injection diesel can be distinguished by having the Bosch name and symbol cast in to the aluminium body of the pump. These pumps usually have “made in Germany” in the cast as well. The fuel supply enters the pump at the opposite end to the injection outlets.

The equivalent CAV/Lucas pump can be identified by the presence of a blue shiny plate with the CAV/Lucas insignia on it. On these pumps the fuel supply enters at the opposite end to the Bosch pump and at the same end as the injection outlets.