In recent years, natural gas has been considered a replacement for diesel fuel in large bore engines, due to its low cost, high heating value and widespread availability. Stoichiometric premixed spark-ignition (SI), defined as port-fuel injection (PFI) of natural gas (NG) followed by SI close to top dead center (TDC), has traditionally been used as the main fuel delivery and combustion method for light and medium duty engines. However, premixed SI of NG results in inefficiencies in the intake process and combustion that is knock limited as boost and load are increased. Traditionally, high knock is addressed by spark timing retard. Spark timing retard can lead to misfires and low brake mean effective pressures. Thus premixed SI has limited low load use in heavy duty where compression ignition of diesel fuel remains dominant. Spark-ignited direct injection (SIDI) of gasoline or GDI has been used for several years in light duty gasoline passenger car engines in combination with turbocharging to extend loads to higher BMEP levels (similar to diesel engines). SIDI method injects fuel during the compression stroke and as a result avoids excessive premixing of fuel and air. SIDI boosted engines can extend load to >20bar bmep and thus results in downsizing of engines to achieve similar power and torque as premixed SI with smaller displacement leading to reduced fuel consumption and reduced CO2 emissions. In this work the single cylinder engine testing was conducted of SIDI of NG using integrated spark injector igniter. The focus of this work is the application of spark ignited direct injection (SIDI) of natural gas for the conversion of heavy duty diesel engines. The influence of DI gaseous injector nozzle spreading angle will be studied. The impact of this parameters on thermal efficiency, specific fuel consumption, combustion stability, combustion phasing, combustion duration and emissions of NOx, HC, CO will be investigated. An optimal nozzle included angle of 100 degrees was determined based on the experimental results which led to the best thermal efficiency as well as good combustion stability.