Biodiesel carbon intensity, sustainability and effects on vehicles and emissions

Published: 2012.01.17

Francisco Posada, Chris Malins, Anil Baral 

This paper summarizes direct and indirect emission and sustainability impacts of biodiesel and assesses the effect of biodiesel blends from the most common feedstocks on compression ignition engine emissions and performance. Key takeaways include: 

  • Existing biodiesel production pathways are unlikely to deliver significant net climate benefits due to indirect emissions. 
  • Models of production have been proposed (e.g ‘Responsible Cultivation Areas’) to avoid indirect emissions from biodiesel production. Jatropha curcuas L. (Jatropha) production carefully planned on land without existing provisioning services could offer meaningful carbon benefits. 
  • Without safeguards, driving biodiesel demand is likely to negatively affect food security and land rights. 
  • Biodiesel expansion is likely to have negative impacts on biodiversity and the local environment, as is expected from any expansion of industrial agriculture. 
  • For both social and environmental risks, there are models of production that would avoid or minimise negative impacts – in particular smallholder focused production models implementing sustainability schemes such as the ‘Roundtable on Sustainable Biofuels’. 
  • Biodiesel will have both positive and negative air quality impacts, depending on the pollutant. Biodiesel reduces emissions of HC, CO and PM. The impact on NOx emissions is less significant and more difficult to predict. An increase in particulate number (PN) is expected from biodiesel blends due to condensation of unburned fuel. 
  • Regarding aldehydes, carbonyls and polycyclic aromatic compounds (PAH) emissions, the amount of information is very limited, especially for Jatropha and other feedstock of interest to India. Thus, research on this area should be conducted, especially for Bharat III and newer engines and vehicles. 
  • It is expected that a particle trap would be highly effective in eliminating nucleation mode particles. Given that biodiesel is virtually sulphur-free, biodiesel would allow the use of DPFs in any Euro III or newer vehicle technology. 
  • Biodiesel is likely to have minor but non-negligible adverse impacts on vehicle reliability. 
  • The use of biodiesel for automotive applications should be developed in collaboration with local automotive manufacturers. Performance and fuel consumption will be reduced with biodiesel compared to diesel, thus new calibrations for similar performance under emissions compliance are required. The effect of antioxidants should be addressed regarding its effect on emissions of criteria pollutants and toxic organic compounds (aldehydes, carbonyls and PAHs). 
  • Production processes like vegetable oil hydrogenation may result in products with better conventional pollutants profiles than fossil diesel across the board, and avoid negative impacts on vehicle reliability.