1. Directive 2009/28/EC of the European Parliament and of the Council of 23 April 2009 on the promotion of the use of energy from renewable sources and amending and subsequently repealing Directives 2001/77/EC and 2003/30/EC.
2. Holm-Nielsen JB, Oleskowicz-Popiel P. The future of biogas in Europe: visions and targets until 2020. In: Proceedings of the European Biogas Workshop –Intelligent Energy Europe, Esbjerg, Denmark, 14–16 June; 2007.
3. Biogas from Waste and Renewable Resources. An Introduction;Deublein,2008
4. Effects of mixing system and pilot fuel quality on diesel–biogas dual fuel engine performance;Bedoya;Bioresource Technol,2009
5. Assessment of simulated biogas as a fuel for the spark ignition engine;Huang;Fuel,1998