A single cylinder research engine has been installed at Bath University for investigation of a stratified charge combustion system for a natural gas engine. The engine has simulated turbocharging and a compressed mains natural gas supply. A relatively complex fuelling system has been developed to enable independent control and measurement of air-fuel ratio to each of the engine's combustion chambers. Results indicate that the emission of oxides of nitrogen may be reduced to very low levels (1-2g/kWh) compared with conventional stoichiometric gas engines (10-2Og/kWh). It has been found that the operation of the prechamber can influence the level of exhaust emission and the cyclic dispersion. Optimum performance is achieved within a relatively narrow range of prechamber supply air:gas ratio from 3:1 to 8:1 by mass.A multi-dimensional fluid dynamic model of the prechamber was developed and used to study the in-prechamber flow structure and mixing processes. The experimental finding on optimum air-gas ratio for the prechamber was supported by the computational study which showed that a pure gas charge leads to an over-rich and highly inhomogeneous mixture at the point of ignition.