Influence of oxygen content of the certain types of biodiesels on particulate oxidative potential

https://doi.org/10.1016/j.scitotenv.2015.12.036Get rights and content

Highlights

  • Oxidative potential is related to the OOA.

  • Oxygen content of the fuel increases the ROS production.

  • Oxygen content of the fuel is correlated with OOA.

  • DTT and BPEA-nit assays agree about the relation of the fuel oxygen content and OOA.

Abstract

Oxidative potential (OP) is related to the organic phase, specifically to its oxygenated organic fraction (OOA). Furthermore, the oxygen content of fuel molecules has significant influence on particulate OP. Thus, this study aimed to explore the actual dependency of the OOA and ROS to the oxygen content of the fuel. In order to reach the goal, different biodiesels blends, with various ranges of oxygen content; have been employed. The compact time of flight aerosol mass spectrometer (c-ToF AMS) enabled better identification of OOA. ROS monitored by using two assays: DTT and BPEA-nit. Despite emitting lower mass, both assays agreed that oxygen content of a biodiesel is directly correlated with its OOA, and highly related to its OP. Hence, the more oxygen included in the considered biodiesels, the higher the OP of PM emissions. This highlights the importance of taking oxygen content into account while assessing emissions from new fuel types, which is relevant from a health effects standpoint.

Introduction

Biodiesel is made of vegetable oils and animal fats and therefore is well known as a renewable source. It has become increasingly important in recent years due to its nature, and because it is more environmental friendly than fossil diesel (Lapuerta et al., 2008a, Lapuerta et al., 2008b). Furthermore, it has a high combustion efficiency of 90–100%, depending on the chemical structure. Biodiesel can be used as either the neat fuel or blended with petroleum diesel. Engine performance and emissions generated using biodiesel is dependent on many factors including: engine load condition; engine type; and engine operation temperature. The majority of published studies have reported lower production of hydrocarbon (HC), PM and CO emission, but higher NOx emission (Lapuerta et al., 2008a, Lapuerta et al., 2008b). It has also been found that, in diesel/biodiesel blend, particle emissions reduce consistently with fuel oxygen content (Rahman et al., 2014). The presence of oxygen in biodiesel molecules causes more complete combustion, promoting the oxidation of the formed soot (Flynn et al., 1999). Study of Ullman et al. (1994) shows that 1% increase in oxygen content leads to 6–7% PM reduction (Ullman et al., 1994). On the other hand, application of biodiesel leads to an increase in emitted NOX and oxygenated hydrocarbons (Staat and Gateau, 1995, Lapuerta et al., 2008a, Lapuerta et al., 2008b). The production costs for biodiesel synthesis can also be very high (Bender, 1999).

A number of studies have investigated the toxicological potential of biodiesel and given warning about replacement of diesel with biodiesel (de Brito et al., 2010, Kooter et al., 2011). The chemical composition of the PM coming from diesel engine running on biodiesel is highly linked to the chemical structure of the fuel. The presence of oxygen atoms in the molecular structure of the fuel plays an important role in changing the levels of the oxygenated toxic species (Lapuerta et al., 2008a, Lapuerta et al., 2008b).

Among the various types of biodiesels, waste cooking biodiesel is the most economical as it is a waste product. As the oxygenated fuel, it is being explored as a potential replacement for diesel in compression ignition engines (Lapuerta et al., 2008a, Lapuerta et al., 2008b, Lin et al., 2011). Lapuerta et al., 2008a, Lapuerta et al., 2008b observed a significant reduction in particle mass emissions while using different blends of waste cooking biodiesel with neat diesel.

Furthermore, methanol and ethanol (Song et al., 2008, Surawski et al., 2009, Sayin, 2010, Yilmaz, 2012) are often used as diesel fuel alternatives in diesel engines. The major problem in ethanol/diesel blends is that it is immiscible with diesel at room temperature. Increasing the amount of ethanol causes a reduction in cetane number and lubricity of these fuel blends (Fernando and Hanna, 2004). Hence, butanol has been drawing the attention of researchers (Szwaja and Naber, 2010, Altun et al., 2011) due to its ability to blend with diesel. Butanol has a higher energy, lower auto ignition temperature and higher cetane number than methanol and ethanol, and thus, is recognised as a more suitable alternative for diesel fuel. Furthermore, butanol is reported as a very promising biofuel as it emits less CO, NOx and soot (Rakopoulos et al., 2010a, Rakopoulos et al., 2010b, Arslan, 2013).

Additives can affect biodiesel production, performance and emission characteristics (Rao and Rao, 2012). Compounds such as triacetin (T) perform as an anti-knocking agent in biodiesel. Triacetin is also able to increase the density and viscosity of the fuel, and to some extent improve the cold flow properties and oxidation stability (Saka and Isayama, 2009) while it can cause decreasing of the flash point, heating value, and cetane number (Casas et al., 2010). 10% of triacetin blended with 90% of coconut oil biodiesel resulted in significant improvement in engine performance (Rao and Rao, 2012).

This study investigates the outcome of using different biodiesels blends, with various ranges of oxygen content, by monitoring the reactive oxygen species (ROS) concentration. To investigate this, two ROS assays were employed. Dithiothreitol (DTT) assay basically allows the determination of particulate ability to catalyse the electron transfer to the oxygen resulting in the superoxide generation. This chemical based assay has been used for measuring the oxidative potential of the ambient PM (Li et al., 2003), diesel exhaust (Kumagai et al., 2002) and ageing process of PM (Li et al., 2009). The second assay, 9,10-bis (phenylethynyl) anthracene nitroxide (BPEA-nit), is a poorly fluorescent compound which turns highly fluorescent upon exposure to Reactive Oxygen species (ROS). ROS is a collective term for various free radicals, molecules and ions. In this case the most important ROS are the superoxide radical (O2radical dot), hydrogen peroxide (H2O2), hydroxyl radical (radical dotOH), alkoxyl radical (ROradical dot), carbon-cantered radicals (Rradical dot) and singlet oxygen (radical dotO2). This assay has been previously applied to detect the ROS related: to combustion-generated aerosols including cigarette smoke (Miljevic et al., 2010a); biomass combustion in a pellet boiler and a logwood stove (Miljevic et al., 2010b); diesel exhaust (Surawski et al., 2009, Stevanovic et al., 2013); and biodiesel exhaust (Stevanovic et al., 2013, Pourkhesalian et al., 2014).

This study has investigated the relationship between the oxygen content of different biodiesels and the oxidative potential (OP) of the created PM2.5. In the scope of this work, we aim to use two well-established ROS assays in order to evaluate their performances in measurements of particulate OP and also their dependency on the oxygen content of the fuel. This study makes an overall assessment for the application of each probe and does not focus on the chemical details of each probes detection procedure.

Section snippets

Engine

A Euro III Cummins engine was operated to generate aerosols. Details on the engine specification are similar as the study by Stevanovic et al. (2013). It was run in the European Stationary Cycle, ESC (DieselNet, 2015). Fig. 1 shows the schematic of the experimental setup.

The ESC test takes 28 min in total. In this cycle, the engine must work for the specified time in every single mode, in order to complete engine speed and load changes in the first 20 s. The particular speed needed to be held to

Results and discussion

The use of biodiesel either neat or blended with diesel can provide reductions in particulate matter (PM) emissions. This reduction has been reported by a number of studies (de Brito et al., 2010, Jalava et al., 2010, Kooter et al., 2011) which investigated the influence of biodiesel on the engine emissions. The reason for this is found in the shorter carbon chain length of these fuels which reduce the amount of the soot formed (Graboski and McCormick, 1998). Soot formation is favoured by high

Conclusion

The results obtained in this study emphasise that biodiesel can potentially cause more toxic emissions than neat diesel. The measured potential is mostly related to the presence and quantity of oxygenated organic compounds in PM. Despite having a lower total mass emission, tested biodiesels caused emissions with higher OP expressed per unit mass of particles. It was found that this effect is directly related to the chemical composition of tested fuels. The presence and quantity of oxygen in

Conflict of interest

The authors declare no competing financial interest.

Acknowledgement

The authors would like to acknowledge the support from the Australian Research Council Discovery Grant (DP120100126). The contribution of Mr. MD Farhad Hossein in the campaign and laboratory assistance from Mr. Noel Hartnett was also appreciated.

References (61)

  • B. Miljevic et al.

    The application of profluorescent nitroxides to detect reactive oxygen species derived from combustion-generated particulate matter: cigarette smoke—a case study

    Atmos. Environ.

    (2010)
  • B. Miljevic et al.

    On the efficiency of impingers with fritted nozzle tip for collection of ultrafine particles

    Atmos. Environ.

    (2009)
  • M. Rahman et al.

    Particle emissions from biodiesels with different physical properties and chemical composition

    Fuel

    (2014)
  • D. Rakopoulos et al.

    Effects of butanol–diesel fuel blends on the performance and emissions of a high-speed DI diesel engine

    Energy Convers. Manag.

    (2010)
  • D. Rakopoulos et al.

    Investigation of the performance and emissions of bus engine operating on butanol/diesel fuel blends

    Fuel

    (2010)
  • S. Saka et al.

    A new process for catalyst-free production of biodiesel using supercritical methyl acetate

    Fuel

    (2009)
  • C. Sayin

    Engine performance and exhaust gas emissions of methanol and ethanol–diesel blends

    Fuel

    (2010)
  • S. Szwaja et al.

    Combustion of n-butanol in a spark-ignition IC engine

    Fuel

    (2010)
  • A. Yang et al.

    Measurement of the oxidative potential of PM2.5 and its constituents: the effect of extraction solvent and filter type

    Atmos. Environ.

    (2014)
  • N. Yilmaz

    Comparative analysis of biodiesel–ethanol–diesel and biodiesel–methanol–diesel blends in a diesel engine

    Energy

    (2012)
  • Q. Zhang et al.

    Experimental study of n-butanol addition on performance and emissions with diesel low temperature combustion

    Energy

    (2012)
  • A.C. Aiken et al.

    Elemental analysis of organic species with electron ionization high-resolution mass spectrometry

    Anal. Chem.

    (2007)
  • M.R. Alfarra et al.

    Identification of the mass spectral signature of organic aerosols from wood burning emissions

    Environ. Sci. Technol.

    (2007)
  • S. Altun et al.

    Effect of n-butanol blending with a blend of diesel and biodiesel on performance and exhaust emissions of a diesel engine

    Ind. Eng. Chem. Res.

    (2011)
  • R. Arslan

    Emission characteristics of a diesel engine using waste cooking oil as biodiesel fuel

    Afr. J. Biotechnol.

    (2013)
  • A. Casas et al.

    Effects of triacetin on biodiesel quality

    Energy Fuel

    (2010)
  • J. Charrier et al.

    On dithiothreitol (DTT) as a measure of oxidative potential for ambient particles: evidence for the importance of soluble transition metals

    Atmos Chem Phys Discuss

    (2012)
  • M.Y. Chung et al.

    Aerosol-borne quinones and reactive oxygen species generation by particulate matter extracts

    Environ. Sci. Technol.

    (2006)
  • J.M. de Brito et al.

    Acute cardiovascular and inflammatory toxicity induced by inhalation of diesel and biodiesel exhaust particles

    Toxicol. Sci.

    (2010)
  • P. DeCarlo et al.

    Investigation of the sources and processing of organic aerosol over the Central Mexican Plateau from aircraft measurements during MILAGRO

    Atmos. Chem. Phys.

    (2010)
  • Cited by (0)

    View full text