Biogas Engine

Biogas is formed in anaerobic digesters where microscopic organisms in the absence of air act on starches and other organic compounds to produce methane and carbon dioxide (approximate molar analysis 60% CH4, 30% CO2, 10% N2).  See the following link => Micro-Scale Biogas Production: A Beginners Guide  if you want to know more about this process.

The proposed engine burning biogas will mechanically be much like the "Dual Pressure Intake Engine". The below diagram and animation describe the operation of this 'Green' engine.

Biogas or Producer Gas Engine
Biogas Engine
(With Low Pressure Direct Induction Fuel System)

In the animation above:

         Light blue = air intake (at 1 atm)
         Navy blue  = biogas or producer gas
                                     (storage pressure  ~ 4 - 10 atm)

       Using an induction system similar to the "Dual Pressure Intake Engine" but with the fuel and air in separate intake runners, one can  boost the volumetric efficiency of an engine running on biogas that is 50 percent methane by about 20%. This engine would not require a supercharger or turbocharger since the boost would be provided by the storage pressure of the fuel.
This would be accomplished by first filling the cylinder with ambient pressure air and then allowing the biogas to top the cylinder to a boosted pressure. The amount of boost would be limited by the stoichiometric balance of the fuel. Boosting volumetric efficiency by taking advantage of the pressurized fuel is important since biogas has a low heat content compared to Natural Gas, for example.
       Also, the kinetic energy of the fuel/air mix will be high due to the large pressure differential between the induced air (~ 1 atm) and the fuel's storage pressure (4-10 atm). This should help the charge burn quicker and more efficiently.

Schematic of Biogas Engine

 (The engine could be SI or CI)
Biogas Fueled Engine

See a similar engine:
'The Dual Pressure Intake Engine'