Comparative study on measurements of formaldehyde emission of methanol/gasoline fueled SI engine

• The measurement methods applied to measure HCHO emission from engines were investigated.
• HCHO emission from an SI engine fueled with different blending ratio was measured.
• Three different methods are proposed to measure the HCHO emission from SI engines.
• Interior reasons of differences on experimental results were analyzed.

The formaldehyde emissions are harmful to human health. It is necessary to investigate and standardize the measurement methods of formaldehyde emissions from vehicles. Based on the principle of different measurements, this study proposes three different measurement methods of formaldehyde emissions from a Spark-Ignition (SI) engine fueled with 0%, 15% and 45% of methanol in volume respectively for M0, M15 and M45. Fourier transform infra-red (FTIR), high performance liquid chromatographic (HPLC) and gas chromatographic (GC) were used to measure the formaldehyde emissions from the test engine on the same engine conditions. Experimental results show that different measurement methods yield significant different results of the formaldehyde emissions, while all the measurements have the consistent trend in the change of formaldehyde emissions when the test engine operates on the different conditions. The formaldehyde emissions measured by FTIR are more than these measured by HPLC and GC, while there were slight differences on the experimental results by the use of HPLC and GC. There are three major factors leading to the different measurement results, respectively for the differences in the spectral characteristics, interferences of other exhaust emissions and the calibration of the tested gas. Compared with FTIR, chromatographic measurements present better separation of formaldehyde emissions with high frequency response, repeatability and good linearity. The formaldehyde emissions could be measured on-line by the use of FTIR, while formaldehyde emissions measured by the chromatographic measurements are absorbed into the 2,4-dinitrophenylhydrazine solution and then detected by the use of GC and HPLC offline. Therefore, HPLC and GC are preferred as the basements on the measurement of formaldehyde emissions, while FITR is preferred as an in-vehicle application.