The aim of this experimental work was to explore the effects of SCR System on NOx reduction in heavy duty diesel engine fuelled with diesel and alcohol blends. The experimental tests were performed in a 6-cylinder, turbocharged heavy duty diesel engine at full load. In the experimental tests diesel, ethanol, methanol and butanol were used as fuel. The alcohol fuel blends were prepared by mixing low sulphur diesel at volumetric rates of between 5 to 15%. The test results showed that SCR system reduce the NOx emissions 42.6% for diesel fuel. The maximum NOx reduction (43.43%) was achieved with 15% methanol–85% diesel fuel (D85M15) blend.<
Keywords: NOx emission; Alcohol; Heavy duty diesel engine
Diesel engine is one of the crucial reason of air pollution such as nitrogen oxides (NOx), hydrocarbons (HC), carbon monoxide (CO), Carbon dioxide (CO2), Smoke opacity, etc . The extinction of petroleum fuels has led researchers to find alternative fuels [2-4]. For enhance the quality of the performance and combustion various fuel additives are recently used in the automotive sector . The most investigated additives are oxygenated fuel additives in diesel engines . Alcohols like as methanol, ethanol, proponal and butanol are preferred as fuels because they can be generated by fermentation of sugar from vegetable materials, like as corn, algae, sugar cane and other plant materials compraising cellulose [7,8]. Alcohol fuels have many advantages such as decrease particulate matter (PM), nitrogen oxides (NOx) and carbon monoxide (CO) exhaust emissions due to the additional oxygen in fuel . There are various studies about the impacts of ethanol, methanol and butanol on diesel engine combustion and emissions [6-14].
Liotta and Montalvio  investigated the impacts of oxygenated fuels on exhaust emissions on heavy duty engines and they found glycol ethers additions have more effect for reducing PM, CO and NOx emissions.
Ajav et al.  explored the impacts of ethanol diesel fuel blends (E5, E10, E15 and E20) on diesel engine emissions and they reported that obtained fuel blends were reduced CO and NOx emissions in a diesel engine operated at a constant speed.
Chao et al.  researched the impacts of fuel additives containing methanol (MCA) on the regulated emissions of heavy duty diesel engine. The neat diesel fuel blended with methanol levels 5, 8, 10 and 15% by volume respectively. And the results noted that the addition of MCA decreased exhaust emissions, such as NOx, PM, and PAHs diesel engine emissions.
Li et al.  explored the impacts of ethanol–diesel fuel blends (5, 10, 15 and 20%) in a single-cylinder diesel engine and the results showed that ethanol-diesel fuel blends were reduced CO, NOx and smoke opacity exhaust emissions with regard to diesel fuel.
Rakopoulos et al.  researched the performance and emission values of ethanol-diesel fuel blends (5% and 10% (by vol.)) on a sixcylinder, turbocharged heavy duty diesel engine. They measured exhaust gas emissions of haevy duty diesel engine and they reported that the ethanol-diesel fuel blends were decreased the smoke density, NOx and CO emissions with regard to neat diesel fuel.
Zhang et al.  measured the emission change with using diesel oxidation catalyst system on diesel engine. They blended diesel fuel with fumigation methanol. They performed the experiments on a 4-cylinder direct-injection diesel engine with 1800 rev/min speed at different five engine loads. They observed that fuel blends decreased nitrogen oxides (NOx), smoke opacity and the particulate mass concentration decreased.
Ozsezen et al.  explored the combustion and exhaust emission values of isobutanol-diesel fuel blends on a heavy duty diesel engine. They blended iso-butanol addition into diesel fuel with ratios 5%, 10% and 15% by volume and they tested fuel blends at the speed of 1400 rpm at 150, 300 and 450 Nm loads. The results showed that when isobutanol- diesel fuel blends were used the NOx emissions decreased compared to diesel fuel.
In this study, the effects of ethanol, methanol and butanol diesel fuel blends on NOx emissions of a 6-cylinder, turbocharged heavy duty diesel engine with and without SCR system was investigated. Ethanol, metanol and butanol were blended with neat diesel fuel at volumetric rates between 5 and 15%.
The experimental tests were performed on a six cylinder, four-stroke, air-cooled turbocharger diesel engine. The technical specifications and schematic diagram of test unit are shown in Table 1 and Figure 1 respectively. A hydraulic dynamometer was used to determine the torque. Technical specifications of dynamometer are given in Table 2. AVL SESAM i60 Fourier Transform Infrared Spectroscopy (FTIR) device was used measuring of exhaust emissions. FTIR device technical characteristics are presented in Table 3. In the after treatment process, selective catalytic reduction, which involves the spraying of urea in the tail pipe, was incorporated to mitigate NOX. The engine is equipped with SCR aftertreatment system (Figure 2). shows schematic diagram of SCR system unit.
|Type||Electonic control system|
|Peak Torque/ Speed (r/min)||1200-1800|
|Rated Speed||2500 rpm|
|Power||184 kW@2500 rpm|
|Torque||1020Nm @1500 rpm|
|Oil Cooler||Turbocharger &aftercooled|
Table 1: Technical specifications of engine.
|Torque range||250-2200 Nm|
|Speed range||0-4500 rpm|
|Body weight||45 kgf|
|Coupling length||400-750 mm|
|Torque arm length||350mm|
Table 2: Tecnical specifications of dynamometer.
|FTIR Spectrometer Data|
|Sampling rate||1 scans per second (1 Hz)|
|Data rate||All measured gas components at 1 Hz|
|Spectral resolution||0.5 cm-1|
|Measurement cell||Gas cell heated to 191 °C (375.8 °F)|
|Response time||t10 to t90 within 1 s (fast response version within 300 ms)|
|Sample flow rate||10 l/min per stream (20 l/min for fast response version)|
|Detector cooling||Liquid nitrogen, 50 ml/h|
|Zero/purge gas||Nitrogen/synthetic air, 0.6–1.5 l/min|
|Compressed air||5–6 bar rel. max. 100 l/min per FTIR stream|
Table 3: FTIR Technical specifications.
In the experiments, diesel, methanol, ethanol and butanol were used as fuel. The fuel blends were prepared by mixing euro diesel at volumetric rates of 5, 10 and 15%. Methanol-diesel blends specified as D95M5, D90M10 and D85M15. Ethanol-diesel blends specified as D95E5, D90E10 and D85E15. Butanol-diesel blends specified as D95B5, D90B10 and D85B15. Before start to test, engine was runned during 15 min using diesel fuel to reach operating temperature. The fuel blends were tested between 1400 rpm to 2400 rpm with interval of 200 rpm in full load conditions. The fuel propertis of diesel fuel, ethanol, methanol and butanol are reported in Table 4.
|Stoichiometric air fuel ratio||15||8.9||6.7||11.2|
Table 4: Fuel properties of diesel, methanol, ethanol and butanol.
The NOx emission mostly regards to nitrogen monoxide NO and nitrogen dioxide NO2 . NO is usually the most abundant NOx and compose more than 70–90% of total NOx in diesel engine exhaust . Alcohol fuel blends were used for further NOx emission study in a diesel engine fitted with SCR system. The variations of nitrogen oxides (NOx) emissions of test fuels with engine speed are demonstrated in the Figures 3-5. Figure 3 shows the NOx emission values of methanol fuel blends with and without SCR system. After applying SCR system, the NOx emission is substantially reduced by 43.12%, 43.3 and 43.43% than D95M5, D90M10 and D85M15 respectively.
In this work, the NOx emission values of ethanol, methanol and butanol additives on a 6-cylinder, turbocharged heavy duty diesel engine with and without SCR system was investigated. The main findigs from this study is aligned below:
After applying SCR system for D85M15, D85E15 and D85B15 fuel blends, the NOx emission is substantially reduced by 46.45%, 45.9% and 45.5% than diesel respectively.
Addition of ethanol, methanol and butanol decrease the NOx emissions with regard to neat diesel. The reason of the reduction may be owing to the increasing oxygen content and lower cetane number of alcohol additives. Lower cetane number of ethanol, methanol and butanol blends precipitates to longer ignition delay, and leading possibly to higher combustion temperature during the premixed combustion mode [3,9].
This work was supported by Republic of Turkey Ministary of Science, Industry and Technology 01146.STZ.2011-2 SAN-TEZ.