Influence of fuel-borne oxygen on European Stationary Cycle: Diesel engine performance and emissions with a special emphasis on particulate and NO emissions
Introduction
Rigorous emission guidelines in many countries have motivated fuel and engine researchers to explore sustainable and cleaner fuels. Oxygenated fuels play an important role to reduce diesel emissions especially diesel soot and PM emissions [1], [2], [3], [4]. Kurtz et al. [5] reported 91–97% reductions in PM emissions with oxygenated fuels. Miyamoto et al. [6] reported significant reductions in diesel emissions with oxygenated fuels and they also reported that the reductions entirely depended on oxygen content in the fuel. Imdadul et al. [7] did engine experiment fuelling with alcohol-biodiesel-diesel blends. The majority of the emissions were reported lower except NO emissions. Khiari et al. [8] conducted experiments with a Pistacia lentiscus biodiesel having 9.9% oxygen. The authors reported significant reductions in CO, THC and particulates at higher engine loads, however, higher NOx emissions were reported with the same biodiesel. Fueling an engine with neat biodiesel fuels from marine microalga Chlorella variabilis and wasteland-compatible Jatropha curcas leads to significant reductions in major diesel emissions include CO, THC and PM emissions compared to diesel, but higher NOx emissions were reported [9]. Hoque et al. [10] produced biodiesels from low-cost feedstocks including used cooking oil and animal fat by the well-known transesterification process. Glycerol is a by-product of during biodiesel production and can be considered one of the promising low-cost feedstocks for producing a wide range of chemicals [11]. Triacetin, a derivative of glycerol is considered to be a good bio-additive [11]. Rao and Rao [12] did engine experiments with biodiesel and triacetin blends and reported lower emissions including NO and smoke emissions. Pathak and Paul [13] did an investigation with biodiesel-triacetin, and biodiesel-ethanol blends and reported lower CO, HC and smoke emissions with all blends at higher loads, but higher NOx emissions. Lacerda et al. [14] also did an investigation with diesel-triacetin and biodiesel-triacetin blends and reported small reductions in CO, O2 and opacity with the blends, but no changes in NOx and CO2 emissions were reported.
The triacetin is considered to be a cost-effective additive as it is derived from transesterified by-product crude glycerol. The tested triacetin was in the pure (99%) form. The authors conducted a miscibility test with triacetin and waste cooking biodiesel and found no phase separation after 96 h. Melero et al. [15] tested several fuel properties of different triacetin-biodiesel blends. Adding 10% triacetin to biodiesel most of the properties were within biodiesel standard limit. After a careful consideration of engine life, the blending percentage in the current investigation was limited to 10 and based on the different properties of a 10% blend, the authors believe that 10% blend will not be harmful to a diesel engine’s life. Moreover, in the present investigation, the tested triacetin contains 99% ester composition.
Diesel engine performance and exhaust emissions with triacetin have been conducted by some researchers. The majority of the published reports showed engine emissions including smoke, unburnt hydrocarbon (UBHC), carbon monoxide, carbon dioxide and oxides of nitrogen (NOx) emissions. However, an exhaustive search in the literature review revealed that the influence of triacetin-waste cooking biodiesel on engine performance and emissions particularly on particle mass and number emissions have not been investigated so far. The target of this investigation was to effectively utilise triacetin as an additive for waste cooking biodiesel and suppress emissions without deteriorating engine performance.
Section snippets
Test engine and fuels
All experimental measurements were conducted with a fully instrumented 6-cylinder turbocharged common rail diesel engine with a compression ratio of 17.3. The engine specifications are listed in Table 1. Fig. 1 shows the schematic diagram of the experimental setup while Fig. 2 shows a photographic image of the test engine. The raw exhaust gas was diluted in a partial flow dilution tunnel. The diluted exhaust gas was directed to a fast aerosol mobility spectrometer DMS500 (Cambustion Ltd.), a
Effect of engine load on fuel-air equivalence ratio
Fig. 4 plots fuel-air equivalence ratio with respect to engine load for the reference diesel and five oxygenated blends. For all fuels, Fig. 4 exhibits four different loads ranging from a quarter to full load each having three different engine speeds (1472 rpm, 1865 rpm, and 2257 rpm). Generally, it can be seen from Fig. 4 that at all speeds, fuel-air equivalence ratio increases with the increase in engine loads. This is associated with the higher amount of fuel injection into the engine cylinder.
Conclusions
This study investigated the role of fuel-borne oxygen on engine performance and exhaust emissions with a number of oxygenated blends using waste cooking biodiesel as a base oxygenated and triacetin as additive under the 13-mode European Stationary Test Cycle. A reference diesel was used for comparison. The results of this investigation may be summarized as follows:
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NO emissions with the oxygenated blends were higher than those of the reference diesel. A maximum of 9% higher NO emissions were
Acknowledgments
The authors would like to thank Australian Research Council (ARC) Linkage Projects funding scheme (project number LP110200158) that supported the current investigation. The authors also would like to thank Mr. Noel Hartnett of QUT, Mr. Andrew Elder of DynoLog Dynamometer Pty Ltd. and Peak3 Pty Ltd. for their help in this investigation. The authors extend their thanks to Dr. Doug Stuart of Eco Tech Biodiesel for the supply of waste cooking biodiesel.
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