Charcoal-Adsorption, Water-Washing, and Air-Dilution Systems to Reduce Diesel Emissions With Special Emphasis on Odor Reduction

Direct injection (DI) diesel engines emit a far more disagreeable exhaust odor than gasoline engines, especially at low temperatures and at idling. There is no proper system of odor reduction in these conditions in DI diesel engines. This study investigated a charcoal-adsorption system to reduce exhaust emissions including odor in a DI diesel engine at idling under no load operations, where exhaust temperatures are low. Low temperature exhaust gas is passed through a charcoal adsorber. Charcoal has the property of adsorbing odorous gas components. Here odor is reduced more than 0.5 points, a significant odor reduction depending on the engine and adsorber conditions. Exhaust noise, nitrogen oxides $(NOx)$⁠, and eye irritation are also significantly reduced with the system. This study further investigated water-washing system for odor reduction in DI diesel engines at low exhaust temperature conditions. Exhaust gas is passed through the water in the water tank of the system. Aldehydes, organic acids, and other oxygenated components, which are the main odorous components in exhaust gases, are dissolved in water reducing exhaust odor significantly. Eye irritation of exhaust gases is also significantly reduced. The water-washing system not only reduces the odor and eye irritation but also carbon dioxide $(CO2)$⁠, carbon monoxide (CO), $NOx$⁠, and smoke are reduced more than 20–30%. The sound level of exhaust gases is also reduced $10–15dB$ with this system. Air dilution is also attempted in this study for odor reduction where a large amount of fresh air is mixed with exhaust gases. Here dilution ratio of 5 is used. Air dilution alone can reduce odor about 0.5 points. However, odor about 1.5–1.6 points (about 60–65%) can be reduced when air dilution is used in combination with charcoal-adsorber and water-washing system, and odor level is lowered below level 2, which is acceptable for all human beings.