Patent ID: 9627858
Date: 2017-04-18
CPC Classifications: F02P,G01J,G01N,H01T

Claim:
1. An observation plug, comprising: a spark plug body that ignites gas in a combustion chamber by means of an electric discharge generated in a discharge gap located in the combustion chamber, wherein the spark plug body includes an observation hole penetrating therethrough in an axial direction at a location dislocated from the discharge gap; an objective optical system which is provided in the observation hole and which has an incident surface which faces toward the discharge gap, thereby including the discharge gap in an observation area of the objective optical system, wherein the objective optical system bends a course of light received from the incident surface and forms an image of the observation area within the observation hole; and a set of light conduction paths provided in the observation hole, wherein the set of light conduction paths causes the image of the observation area, which is to be formed by the objective optical system, to be divided into a plurality of portions and transmitted therethrough.