Hydrocarbons and aldehydes from a diesel engine running on ethanol and equipped with EGR, catalyst and DPF

摘要

A commercially available exhaust aftertreatment system, DNO{sub}x comprising exhaust gas recirculation (EGR), an oxidative catalyst and a continuously regenerating diesel particulate filter (DPF) were tested. The test object was a 9-liter, ethanol-fueled diesel engine from Scania equipped with turbocharger and aftercooler. A similar diesel engine from Scania, but running on ordinary Swedish diesel fuel, was used as a reference and a reminder of "the state of the art". The tests involved two different ethanol fuels containing various ignition improvers, Beraid 3540 and rapeseed methyl ester. Test conditions for the engines were those specified in the European Stationary Cycle (ESC). The aftertreatment system reduced the emissions of HC, CO and NO{sub}x, down to 0.15, 0.04 and 2.54 g/kWh, respectively, while the estimated particle mass was reduced by 67%. Actually, by using the DNO{sub}x system, the engines became Euro IV engines regarding the emissions of HC, CO and NO{sub}x. The ethanol-fueled engine without EGR, catalyst or DPF emitted approximately 1.6 times more formaldehyde and 9.8 times more acetaldehyde than the diesel engine. However, the emission of acrolein was only 0.47 times the emission of acrolein from the diesel engine. When the ethanol-fueled engine was equipped with DNO{sub}x a significant reduction of the emissions of aldehydes was obtained. The emissions of acrolein, formaldehyde and acetaldehyde were reduced by 56%, 87% and 95%, respectively. An even higher reduction was observed when the system was connected to the diesel engine. Fifteen different hydrocarbons (alkanes, olefins and monoaromates) were also identified. The diesel-fueled engine, without any exhaust aftertreatment devices, emitted approximately twice as much hydrocarbon than the ethanol-fueled engine, also without any exhaust aftertreatment devices. However, there were also qualitative differences. Three hydrocarbons, namely propene, ethene and benzene, accounted for 77% of the hydrocarbons emitted from the diesel-fueled engine, while acetylene, ethene and benzene, made up only 53% of the hydrocarbons emitted from the ethanol-fueled engine. When connecting the system to the engines, a difference was observed; the reduction of analyzed hydrocarbon emissions was approximately 90% for the diesel-fueled engine, but only 47% for the ethanol-fueled engine. The studied aftertreatment system has been developed and optimized for the diesel-fueled engine. This fact is reflected in the powerful reduction of hydrocarbons, aldehydes, particles and NO{sub}x that is obtained when connecting the system to the diesel-fueled engine. Nevertheless, a significant reduction is also obtained when connecting the system to the ethanol-fueled engine. Test results indicate that it should be possible to better optimize the system for the ethanol engine. It is also, probably, necessary to exchange the catalyst in the system. Thereby, an even higher reduction of unregulated and regulated emissions should be obtained.