26-07-2012, 03:58 PM
Diesel Engine Emission Control
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Abstract
Oxygenated diesel fuel blends have a potential to reduce the emission of particulate matter (PM) and to be an alternative to diesel fuel. This paper describes a new kind of oxygenate additive, ethylene glycol monoacetate (EGM), and its effects on the characteristics of performance and emission of a compression ignition engine. The results show that the engine power outputs decrease and the BSFC increase when the diesel engine fueled with blends, but the diesel equivalent BSFC decrease. The results also indicate that all oxygenated fuels tested in this study show a beneficial effect on reducing smoke emissions at the operation conditions compared with diesel fuel. With the EGM15, an average smoke reduction of 49.9% and a maximal smoke reduction of 71% are obtained. The blends have little effects on the NOx emissions at most loads. The CO emissions of the EGM diesel blends decrease obviously at high load. The second paper investigated particulate matter (PM) and NOx removal using nonthermal plasma chemical hybrid processes without using catalysts. Among nonthermal plasma hybrid processes, the ozonizer combined with the chemical hybrid reactor was investigated using a 479 cc (5.5 kW) power generation diesel engine. The PM deposited on the diesel particulate filter can be incinerated by ozone and NO2 in a wide range of flue gas temperature. The NO was oxidized to form NO2 by ozone, and NO2 was reduced by the 3% Na2SO3 chemical reactor. The rate of PM incineration depends on the amount of ozone injected and was significantly higher than the rate of PM generation. Using 2.4% ozone concentration with a flow rate of 10 L/min, 82% of NO having 720 L/min was oxidized to NO2, and 78% of NOx was removed as a chemical scrubber. However, NOx removal was deteriorated about 10% after 1-h operation. This was attributed to Na2SO3 oxidation by air, which was evidenced by the reduction of pH in the chemical reactor.
Keywords-ethylene glycol monoacetate (EGM); Diesel particulate filter (DPF), nonthermal plasma, particulate matter (PM).
I. INTRODUCTION
Particulate matter emissions from diesel engines are a public health concern that has prompted research on fuel formulations and technologies to reduce soot formation. It is thought that reformulated diesel fuels will play an important role. The reformulation of diesel fuels could include lowering the sulfur content, lowering the aromatic content, or potentially the addition of oxygen within the fuel. It has been shown that many oxygenates are effective in reducing particulate emissions from diesel engines. Ethylene glycol monoacetate (EGM) is regarded as one of the promising alternative fuels or oxygen additives for diesel engines, with high oxygen content. As one of the radical injections, the ozone injection combined with the chemical hybrid reactor was investigated using a 479 cc (5.5 kW) power generation diesel engine (J106-STD Kubota Corporation). The PM deposited on both metal and ceramic diesel particulate filters (DPFs) was incinerated by ozone and NO2, and PM removal was evaluated at various gas temperatures. The rate of PM incineration depends on the amount of ozone injected and the ozonizer using oxygen and air was investigated. The NO was oxidized to form NO2 by ozone at various flue gas temperatures and NO2 was reduced by the chemical reactor using a 3% Na2SO3. The condition of continuous operation was evaluated by monitoring pH in scrubber solution.
II. EXPERIMENTAL SETUPS
A commercial light-duty direct injection diesel engine 4JB1 is used in this study, made by Beiqi Foton Motor Co. Ltd., which is a 4-stroke, 4-cylinder, naturally aspirated diesel engine. Engine Specifications are shown in Table II. An ultrasonic mixer is used to blend various EGM and diesel fuels in real-time as they flow to the engine. The power and frequency of the ultrasonic mixer are 100W and 40Hz, respectively.
Schematic diagram of the ozone injection and a chemical process for the diesel emission control. Flue gas was generated from a 5.5-kW diesel engine (J106-STD, Kubota Corporation) with a full load, which generates 720 L/min and 670 ppm of NOx (605 ppm of NO and 65 ppm of NO2). The gas concentrations such as NO, NO2, NOx, CO, CO2, O2, and gas temperature, which were varied with the load by placing the electric heaters, were monitored. Ozone was generated by the ozonizer (Masuda Research OZS-HC-70/W) using the surface discharge with 10–11 kHz ac. either oxygen or air as for more practical application was used as media to achieve a desired ozone concentration.
An electric eddy dynamometer, made by Xiangyi Power Instrument Co. Ltd, is coupled to the engine and used to measure the engine power. Smoke is measured by a partial flow smoke opacimeter (AVL Di Smoke 4000). NOx, CO and HC are measured by exhaust gas analyzer (AVL Di Gas 4000). The schematic of the experimental setup is shown in Fig. 1. The coolant temperature is kept at 80 during the experiment.
III RESULTS AND DISCUSSION
The brake specific fuel consumption (BSFC) measurements for different EGM-diesel blends and pure diesel fuel at speed of 3600r/min are shown in Fig. 2. At low load, the BSFC slightly increases with the EGM addition to diesel. At medium and high loads, the BSFC for the EGM-diesel blends is about the same to that for diesel. The differences in BSFC reflected the differences in some of the physical properties of the fuels such as density and low heating value. Low heating value of EGM is lower than that of diesel fuel. The low heating value of diesel is 42.5 MJ/kg, whereas that of EGM2, EGM5, EGM10 and EGM15 is 42.17, 41.68, 40.85 and 40.03MJ/kg, the drop is about 0.8%, 1.9%, 3.9% and 5.8%, respectively.
In theory, the BSFC should increase with an increase in the oxygenate content in the fuel blends because of the reduced energy content. In the current study, the fuel blends show very slight increase in BSFC compared with diesel fuel, particularly at higher loads. Therefore, it can be concluded that the addition of EGM in diesel can improve the combustion process. These facts become more clearly when the diesel equivalent BSFC is
Used, as shown in Fig.3. The diesel equivalent BSFC decreases when engine fueled with EGM-diesel blends. The maximum drop of diesel equivalent BSFC for EGM15 compared to pure diesel fuel is 3.9%
Fig.3 illustrates the smoke emission under various loads at the speed of 3600r/min. It is obvious that the smoke emission can be remarkably reduced with the EGM addition to diesel, and is decreased most with EGM15. Adding oxygenates to diesel fuel has a remarkable effect on the reduction of smoke emissions, especially at high load. With the EGM15, an average smoke reduction of 49.9% and a maximal smoke reduction of 71% are obtained under this condition. The reduction of smoke emissions can be explained by the enrichment of oxygen content in the fuel by the addition of oxygenates (EGM), resulting in more complete combustion.
Fig. 4 gives the NOx emissions for different fuels at the speed of 3600r/min. In general, the addition of EGM in diesel has little effects on the NOx emission at most loads. But at very lower loads, NOx emissions of EGM-diesel blends increase with increase in the fraction of EGM in the blends. The cetane number value of EGM is lower than that of diesel, and the latent heat of vaporization of EGM is higher than that of diesel. The lower cetane number value and the higher latent heat of vaporization mean an increase in the ignition delay and more accumulated fuel/air mixture, which cause a steep heat release in the beginning of the combustion, resulting in high temperatures and high NOx formation. This phenomenon is obvious at very lower loads.
In case of CO emission shown in Fig. 5, the CO emissions of the EGM-diesel blends slightly increase at low load, while they decrease obviously at high load with increase in the fraction of EGM in the blends.
The ozone concentration, which depends on power, flow rate, and media, becomes 50.7 g/m3 with oxygen and 18.0 g/m3 with dry air when 10 L/min was introduced into the ozonizer.
Ozone was injected into 350 ◦C flue gas right after the diesel engine for PM removal. For NOx removal, the flue gas was cooled down with the water spray cooler in the duct and pass through two sets of 160-L polypropylene tank as the scrubber, where 3% of Na2SO3 solution was used as reducing chemical. The following chemical reaction takes place (2 NO2 + 4 Na2SO3 → 4 Na2SO4 + N2).
The experiments consist of three parts: PM removal with O3 injection at high and low temperature, and NOx removal with Na2SO3 solution.