Dilution air refine system used in formaldehyde measurement

The intention of this paper is to demonstrate the advantages of the dilution air refine (DAR) system used in emission test for low emission vehicles, especially for formaldehyde emission test. Based on the DAR system, emissions from a passenger car fueled with methanol/gasoline blends (M15) were investigated. The car was tested over the New European Driving Cycle (NEDC). The typical legislated emissions were tested by a Horiba MEXA-7400LE motor exhaust gas analyzer. Formaldehyde was trapped on 2, 4-dinitrophenylhydrazine (DNPH)-coated silica cartridge and analyzed by high performance liquid chromatography (HPLC). Methylbenzene was sampled by Tenax TA and analyzed by thermal desorption-gas chromatography/mass spectrometer (TD-GC/MS). Results indicate that, compared to traditional CVS system, DAR can improve the measurement accuracy by decreasing and even eliminating the background concentration of dilution air, what's more, it can improve the measurement accuracy of formaldehyde emission effectively which makes DAR to be the preferred test system in measurement of unregulated emissions from light duty vehicles. And on this basis, pollutant emissions from the car fueled with methanol/gasoline blends were investigated. Results show that the car fueled with methanol/gasoline blends (M20/M30/M50) decreased the THC and CO by 39.68-46.98 % and 63.16-65.75 % respectively while increased the NO_X by 128.91-191.94 %. For unregulated pollutants, methanol/gasoline blends produce formaldehyde 12.06-77.59 % more than the baseline gasoline but the methylbenzene is 34.65-68.73 % less than that. The limitation of this study is that the measurements should be based on more vehicles to get much more exact data. This paper introduces the advantages of the dilution air refine system for the first time which are not mentioned in other papers before. The conclusion of this paper is that the DAR system can improve the measurement accuracy effectively especially for formaldehyde test and the methanol/gasoline blends produce less regulated pollutants and more formaldehyde. This problem can be solved by using additives and new three-way catalytic converters.