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Energy & Fuels 2007, 21, 3310–3316
NOx and Particulate Matter (PM) Emissions Reduction Potential by Biodiesel Usage Breda Kegl* UniVersity of Maribor, Faculty of Mechanical Engineering, SmetanoVa 17, SI-2000 Maribor, SloVenia ReceiVed May 11, 2007. ReVised Manuscript ReceiVed July 4, 2007
The transport in many countries is the most significant source for NOx and particulate matter (PM) emissions. Therefore, the possibility of reducing NOx and PM emissions is experimentally investigated using biodiesel and some of its blends with mineral diesel. Attention is focused on the optimal bus diesel engine adjustments for each tested fuel. The obtained engine characteristics are compared to each other by considering the 13 modes of the European stationary cycle test. The optimal injection pump timings are determined with the aim of reducing harmful emissions, while keeping other engine characteristics within acceptable limits. The optimal fuel blend is suggested, and the harmful emissions (NOx, PM, CO, unburned hydrocarbon, and smoke) reduction is estimated.
1. Introduction The key factors of diesel engine development are related to engine performance, economy, and ecology. In recent years, enviable results have been achieved with new electronically controlled high-pressure fuel injection systems and after treatment technologies.1 Despite respectful achievements, a further reduction of engine emissions is still necessary because ecology regulations become every day more and more stringent.2,3 Furthermore, the independence on imported petroleum sources becomes ever more important.4 For this reason, over the past years, the investigations on diesel engines have expanded in the area of alternative fuels, which are renewable, available locally, and cleaner than mineral diesel.5 Among alternative fuels, biodiesel represents a very promising fuel. Biodiesel is a sulfur-free, nontoxic, biodegradable, oxygenated, and renewable fuel. In the near future, various biodiesel fuels, such as ethyl or methyl esters from soybean oil, rapeseed oil, sunflower oil, etc., offer a potentially very interesting alternative regarding harmful emissions, engine wear, cost, and availability.6,7 Mostly, biodiesel is made from soybean oil in * To whom correspondence should be addressed. E-mail: breda.kegl@ uni-mb.si. (1) Wallace, F. J.; Hawley, J. G. Analysis of the effect of variations in fuel line pressure in high-speed direct injection diesel engines, with highpressure common rail fuel injection systems on heat release, cylinder pressure, performance, and NOx emissions. Proc. Inst. Mech. Eng., Part D: J. Automobile Eng. 2005, 219, 413–422. (2) Fernando, S.; Hall, C.; Iha, S. NOx reduction from biodiesel fuels. Energy Fuels 2006, 20, 376–382. (3) Erisman, J. W.; Grennfelt, P.; Sutton, M. The European perspective on nitrogen emission and deposition. EnViron. Int. 2003, 29, 311–325. (4) Durbin, T. D.; Collins, J. R.; Norbeck, J. M.; Smith, M. R. Effects of biodiesel, biodiesel blends, and a syntetic diesel diesel on emissions from light heavy-duty diesel vehicles. EnViron. Sci. Technol. 2000, 34, 349– 355. (5) Canakci, M. Combustion characteristics of a turbocharged DI compression ignition engine fueled with petroleum diesel fuels and biodiesel. Bioresour. Technol. 2007, 98, 1167–1175. (6) Dorado, M. P.; Ballesteros, E.; Arnal, J. M.; Gomez, J.; Lopez, F. J. Exhaust emissions from a diesel engine fueled with transesterfified waste olive oil. Fuel 2003, 82, 1311–1315. (7) Boehman, A. L.; Song, J.; Alam, M. Impact of biodiesel blending on diesel soot and the regeneration of particulate filters. Energy Fuels 2005, 19, 1857–1864.
the United States and from rapeseed oil in Europe. In comparison to mineral diesel, biodiesel fuels have comparable energy density and cetane number; they have little sulfur and much oxygen.8,9 However, high viscosity, high molecular weight, low volatility, etc. of biodiesel may in some cases lead to problems such as severe engine deposits, injector cooking, and piston ring sticking.6,10–12 Most of the currently working diesel engines have been developed for operation with mineral diesel. For these engines, biodiesel can obviously not be used without any precautions. Therefore, many investigations are necessary to prevent or at least mitigate different diesel engine or environmental problems. In general, many researchers agree that biodiesel, derived from various sources, causes a decrease of unburned hydrocarbon (HC), CO, and particulate matter (PM) emissions. This can be observed on various diesel engines. Furthermore, higher sound velocity of biodiesel, which results in the advanced fuel injection timing, increases the NOx emission.6,13–15 Although the investigations confirm the above trends in general, one must say that the obtained results vary significantly depending upon the fuel, engine, engine(8) Dwivedi, D.; Agarwal, A. K.; Sharma, M. Particulate emission characterization of a biodiesel vs diesel-fuelled compression ignition transport engine: A comparative study. Atmos. EnViron. 2006, 40, 5586– 5595. (9) Shi, X.; Pang, X.; Mu, Y.; He, H.; Shuai, S.; Wang, J.; Chen, H.; Li, R. Emission reduction potential of using ethanol–biodiesel–diesel fuel blend on a heavy-duty diesel engine. Atmos. EnViron. 2006, 40, 2567– 2574. (10) Canakci, M. Performance and emissions characteristics of biodiesel from soybean oil. Proc. Inst. Mech. Eng., Part D: J. Automobile Eng. 2005, 219, 915–922. (11) Knothe, G.; Steidley, K. R. Kinematic viscosity of biodiesel fuel components and related compounds, Influence of compound structure and comparison to petrodiesel fuel components. Fuel 2005, 84, 1059–1065. (12) Dorado, M. P.; Ballesteros, E.; Arnal, J. M.; Gomez, J.; Gimenez, F. J. L. Testing waste olive oil methyl ester as a fuel in a diesel engine. Energy Fuels 2003, 17, 1560–1565. (13) Leung, D. Y. C.; Luo, Y.; Chan, T. L. Optimization of exhaust emissions of a diesel engine fuelled with biodiesel. Energy Fuels 2006, 20, 1015–1023. (14) Kegl, B. Experimental investigation of optimal timing of the diesel engine injection pump using biodiesel fuel. Energy Fuels 2006, 20, 1460– 1470. (15) Kegl, B. Numerical analysis of injection characteristics using biodiesel fuel. Fuel 2006, 85, 2377–2387.
10.1021/ef7002393 CCC: $37.00 2007 American Chemical Society Published on Web 09/05/2007
NOx and PM Emissions Reduction Potential
Energy & Fuels, Vol. 21, No. 6, 2007 3311
Table 1. Some Properties of Biodiesel and Diesel Fuel fuel
D2
B100
kinematic viscosity at 40 °C (mm2/s) surface tension at 40 °C (N/m) lower calorific value (kJ/kg) cetane number
2.64 0.0252 43.800 45–55
4.42 0.0265 38.177 >51
operating regime, and injection system used. This necessitates various strategies to reduce harmful emissions. These are related, for example, to the transesterification process, combined with the peroxidation technique, to the retarted injection timing, or to exhaust gas recirculation.2,9,13,15–20 The work in this paper is a continuation of our experimental and numerical investigations of the influence of neat biodiesel from rapeseed oil on the characteristics of a bus diesel engine.14,15,17,21 In particular, the paper focuses on the performance of some biodiesel/mineral diesel blends. Furthermore, in contrast to our previous work, PM emission is also determined and taken into account. Attention is focused on the determination of optimal injection pump timing for tested fuels with the aim to reduce all engine harmful emissions, especially NOx and PM. The measured engine characteristics are compared against those obtained using mineral diesel at several engine-operating regimes. 2. Tested Fuels The fuels under consideration are (i) neat mineral diesel (D2), conforming to European standard EN 590, (ii) neat biodiesel, here denoted as B100, conforming to European standard EN 14214, and (iii) their blends BXX, where XX denotes the vol % of biodiesel (e.g., B25 consists of 25 vol % of biodiesel and 75 vol % of mineral diesel). All of the tested fuels do not contain any additives for winter conditions. Some measured properties of these fuels are given in Table 1. The biodiesel used in this work is produced from rapeseed by Pinus, Slovenia. Some of its specifications are given in Table 2. Fuel properties have a noticeable influence on the engine characteristics. For this reason, the most important properties of tested fuels have been determined experimentally. The fuel density, obtained by our experiment at ambient pressure, is presented in Figure 1. One can see that the density increases by increasing the content of B100 and by decreasing the fuel temperature. The measurement of sound velocity in fuel was based on the principle of pressure wave propagation in the high pressure (HP) tube. The tube is instrumented by two piezoelectric pressure transducers, located at both ends of the tube. The sound velocity was measured at different pressures, up to 400 bar, using different fuels. Figure 2 shows the dependence of sound velocity at a fuel temperature of 20 °C. One can see that, by increasing the pressure and biodiesel content, the sound velocity also (16) Corrêa, S. M.; Arbilla, G. Aromatic hydrocarbons emissions in diesel and biodiesel exhaust. Atmos. EnViron. 2006, 40, 6821–6826. (17) Kegl, B.; Hribernik, A. Experimental analysis of injection characteristics using biodiesel fuel. Energy Fuels 2006, 20, 2239–2248. (18) Lin, C. Y.; Lin, H. A. Diesel engine performance and emission characteristics of biodiesel characteristics of biodiesel produced by the peroxidation process. Fuel 2006, 85, 298–305. (19) Nabi, N.; Akhter, S.; Shahadat, M. Z. Improvement of engine emissions with conventional diesel fuel and diesel–biodiesel blends. Bioresour. Technol. 2006, 97, 372–378. (20) Tsolakis, A.; Megaritis, A. Exhaust gas assisted reforming of rapeseed methyl ester for reduced exhaust emissions of CI engines. Biomass Bioenergy 2004, 27, 493–505. (21) Kegl, B. Effects of biodiesel on emissions of a bus diesel engine. Bioresour. Technol. 2007, 10.1016/j.biortech.2007.01.021.
Table 2. Specification of B100
ester content % (m/m) sulfur content (mg/kg) carbon residue on 10% distillation residue % (m/m) water content (mg/kg) oxidation stability, 110 °C (h) acid value (mg of KOH/g) iodine value (g of I2/100 g) linolenic acid methyl ester % (m/m) methanol content % (m/m) free glycerol % (m/m) total glycerol % (m/m)
biodiesel, Pinus
European standard for biodiesel, EN 14214
96.9
