Spark plug with combustion sensor

A spark plug assembly, comprising:

• a generally annular ceramic insulator having an annular surface extending between an upper mast portion and a lower distal end, said annular surface transitioning via a shoulder to a reduced diameter nose portion;
• a metal annular outer shell surrounding at least a portion of said ceramic insulator;
• a ground electrode operatively attached to said outer shell;
• a center electrode received in said ceramic insulator, said center electrode extending between an upper terminal end and a lower firing end, said lower firing end extending out of said nose portion of said insulator, said lower firing end of said center electrode and said ground electrode providing a spark gap;
• a force sensor disposed about said insulator;
• an annular inner shell received between said outer shell and said insulator, said inner shell having a first surface configured to confront said shoulder of said insulator along an axial direction;
• wherein said inner shell extends to a lower end, said inner shell being fixed to said outer shell adjacent said lower end and the remaining portion of said inner shell remaining spaced from said outer shell by a gap;
• and
• said inner shell has a radially outwardly extending shoulder and said outer shell has a radially outwardly extending flange, said shoulder and said flange being axially spaced from one another by said gap.