The authors present a portable NH3 and N2O analyzer utilizing mid-infrared laser absorption spectroscopy for on-board emission measurements. The developed analyzer employs a newly developed absorption spectroscopy named “infrared laser absorption modulation”, hereinafter referred to as IRLAM, for the signal acquisition and concentration determination. Because of IRLAM’s simple and robust signal processing scheme, a highly sensitive, selective and robust measurement system can be realized within a compact size.
The following performance metrics of the new analyzer are presented: linearity, detection limit, response time and zero/span drift. Notably, the detection limit (defined as 2σ of the zero signal) of ≤ 0.1 ppm is achieved in both NH3 and N2O measurements.
The influence of vibration, and changes in environment conditions such as ambient temperature and atmospheric pressure, are also tested. The effect of random vibrations had little observable impact on the measurement noise level. In the temperature test from −10 °C to 50 °C, the change in measured values is within ±1% of the span concentration. The ambient pressure test to simulate atmospheric pressure changes shows that the change in measured values from 0 to 2,500 m altitude is less than 1%.
In order to verify that the new portable analyzer can be used for real emission measurements, a correlation test was conducted between the portable analyzer and a stationary quantum cascade laser-based emission analyzer on an engine test bench. The result shows a strong correlation between the two analyzers, with the determination coefficient of 0.9889 for NH3 and 0.9935 for N2O. Moreover, the analyzer was mounted on a vehicle and an on-road driving test was conducted, the results of which gave insight into the emission behaviors of NH3 and N2O during the on-road driving.