Article pubs.acs.org/est
Evaluation of the Impacts of Biodiesel and Second Generation Biofuels on NOx Emissions for CARB Diesel Fuels Maryam Hajbabaei,† Kent C. Johnson,† Robert A. Okamoto,‡ Alexander Mitchell,‡ Marcie Pullman,‡ and Thomas D. Durbin*,† †
Department of Chemical, Environmental Engineering, Bourns College of Engineering, Center for Environmental Research, Technology (CE-CERT), University of California, Riverside, California, United States ‡ California Air Resources Board, 1001 “I” Street, P.O. Box 2815, Sacramento, California 95812, United States S Supporting Information *
ABSTRACT: The impact of biodiesel and second generation biofuels on nitrogen oxides (NOx) emissions from heavy-duty engines was investigated using a California Air Resources Board (CARB) certified diesel fuel. Two heavy-duty engines, a 2006 engine with no exhaust aftertreatment, and a 2007 engine with a diesel particle filter (DPF), were tested on an engine dynamometer over four different test cycles. Emissions from soy- and animal-based biodiesels, a hydrotreated renewable diesel, and a gas to liquid (GTL) fuel were evaluated at blend levels from 5 to 100%. NOx emissions consistently increased with increasing biodiesel blend level, while increasing renewable diesel and GTL blends showed NOx emissions reductions with blend level. NOx increases ranged from 1.5% to 6.9% for B20, 6.4% to 18.2% for B50, and 14.1% to 47.1% for B100. The soy-biodiesel showed higher NOx emissions increases compared to the animal-biodiesel. NOx emissions neutrality with the CARB diesel was achieved by blending GTL or renewable diesel fuels with various levels of biodiesel or by using di-tert-butyl peroxide (DTBP). It appears that the impact of biodiesel on NOx emissions might be a more important consideration when blended with CARB diesel or similar fuels, and that some form of NOx mitigation might be needed for biodiesel blends with such fuels.
■
renewable fuels standard,4 and on a regional or state level, such as the California Air Resources Board’s (CARB) Low Carbon Fuel Standard (LCFS).5 Biodiesel is the most widely used biofuel in diesel engines, and it is currently the main fuel being used or considered to meet renewable fuel requirements for diesel fuel. Biodiesel is currently used at a 7% level in diesel fuel throughout Europe.6 Biodiesel use and production in the U.S. has expanded considerably over the past decade, 7 from 2 million gallons in 2000 to 1.1 billion gallons in 2011.8 Studies have shown that biodiesel generally reduces carbon monoxide (CO), particulate matter (PM), and total hydrocarbons (THC) emissions compared to conventional diesel fuel.9−13 It has also been reported in many studies, however, that average nitrogen oxides (NOx) emissions from biodiesel blends can increase with increasing biodiesel content. Although the impact of biodiesel on NOx emissions has been studied for many years, there is still
INTRODUCTION The development and implementation of renewable and sustainable fuels for transportation applications is a critical element in meeting a number of different environmental and other challenges. The transportation sector is one of the largest sources of manmade carbon dioxide (CO2) emissions, which comprise the largest component of greenhouse gas inventories and can lead to global climate change.1 There is also a need to diversify from fossil fuel resources, which will not be sustainable as a long-term source of energy. The importance of these issues is further emphasized by the continuing expansion of transportation fuel use in less developed countries and areas, and associated projections that the use of transportation fuels will continue to increase going into the foreseeable future.2 In the face of these issues, governmental regulations have been, and are being developed, worldwide to promote the use of increasing levels of biofuels, which can be produced from sustainable sources and can reduce CO2 emissions when a complete carbon life cycle is considered. These regulations are being developed on a multinational level, such as the European regulations,3 on a national level, such as the United States (U.S.) Energy Independence Act of 2007 and the associated © 2012 American Chemical Society
Received: Revised: Accepted: Published: 9163
February 22, 2012 June 29, 2012 July 12, 2012 July 12, 2012 dx.doi.org/10.1021/es300739r | Environ. Sci. Technol. 2012, 46, 9163−9173
Environmental Science & Technology
Article
Table 1. Selected Fuel Propertiesa API gravity (@ 60 °F) density (@ 60 °F) aromatics, mass % PAHs, mass % cetane number sulfur, ppm carbon, % wt. hydrogen, %wt. oxygen, % wt. C/H ratio cloud point, °C pour point, °C distillation, °F ibp 10% 50% 90% ep distillation, T90 AET, °C heat value a
test method
CARB diesel
renewable diesel
GTL
soy-biodiesel
animal-biodiesel
D287-82
39.3 0.827 18.7 1.5 55.8 4.7 86.1 13.67 0.23 6.3 −6.6 −12
51.3 0.771 0.4 0.1 72.3 0.3 84.83 15.14 0.03 5.6 −27.1 −47
48.4 0.786 0.5
