It is completely possible to run a diesel engine on biogas; however, a number of considerations must be taken into account before it may be considered a serious option in a development program. This article will explore some key considerations when attempting to burn biogas in a diesel engine.
First, it is important to distinguish between different types of diesel engines. Diesel engines are pretty similar in operation and have been around since Rudolf Diesel first developed the engine in the 1800’s. They rely on compression ignition (CI) of a small amount of diesel fuel that is injected into the ignition chamber. Simultaneously, a valve is opened to allow air into the ignition chamber. The valve is closed and the piston compresses the mixture. When the air/fuel mix reaches its ‘stoichiometric point’ (i.e. the point at which the ratio of fuel:air is enough to chemically combust), it ignites under the pressure created when the piston reaches Top Dead Centre (TDC), which is normally around a 17:1 compression ratio. As the mixture ignites, the piston is forced downwards, driving the connecting rod and thus turning the engine. Modern diesel engine cars have sophisticated fuel systems and engine management systems that make the engine very efficient but more ‘highly strung’; the introduction of an impure gas (such as biogas) into the equation will result in problems.