Measurement of temperature of spark-discharge plasma in engine cylinder

Abstract

The vibrational and rotational temperatures in a spark-discharge plasma were measured using optical emission spectroscopy in the cylinder of an engine operating at 1000 rpm. Based on the observed spectrum, the nitrogen molecule emissions from 370 to 385 nm were measured in an air atmosphere without fuel injection. The plasma temperatures were estimated by fitting a theoretically calculated spectrum. When the spark discharge timing was retarded, an unknown band head (different from that corresponding to nitrogen molecule emissions) appeared. This made temperature estimation difficult. Two experiments were performed in an attempt to examine the origin of the unknown band head. One involved using a pure nitrogen atmosphere, instead of air, in the cylinder. However, due to the appearance of a strong nitrogen ion band head, part of the nitrogen molecule spectrum could not be identified. The second experiment addressed the emissions from the spark plug electrodes. The band head was presumed to be a result of emissions from Fe, Ir, Rh, and Cr. The experiment was performed using a spark-plug with electrodes with reduced amounts of these elements. The band head for temperature measurement was hidden by unknown band heads. As a result, estimation of the temperatures in the plasma was not possible later than the discharge timing of 60 ° BTDC. At a discharge timing of 60 ° BTDC (ambient pressure = 0.25 MPa, ambient temperature = 390 K, flow rate = 20 m/s), the vibrational temperature in the spark-discharge plasma was 9200 K while the rotational temperature was 2300 K.

Keywords

• plasma temperature
• spark discharge
• si engine
• optical emission spectroscopy
• nitrogen molecure