Abstract: A spark plug includes an insulator body provided with a longitudinally-extending through bore. A one-piece, central electrode is secured within the longitudinally-extending through bore, while simultaneously providing an annular zone communicating with a combustion chamber. An earth lower electrode projects diametrically-inward towards the central electrode and is spaced a longitudinally-fixed distance beyond the lower end of the central electrode. A first, non-central longitudinally-extending bore in the insulator body is connected to a fuel metering device for controllably admitting fuel to the combustion chamber. A second, non-central, longitudinally-extending bore in the insulator body is connected between the combustion chamber and an exhaust manifold to exhaust gases from the combustion chamber. A lower-threaded base connects the spark plug to an opening in the combustion chamber.