a low emissions 2 - stroke natural gas fueled engine includes at least one cylinder with an exhaust port in communication with a silencer / catalytic converter unit . the unit has first and second volumes in communication with each other . the first volume dampens spurious exhaust pressure excursions and removes particulates in the exhaust . the second volume houses an oxidation catalyst for treating exhaust to reduce exhaust emissions . the engine oil has at most 10 ppm zinc content to reduce metal poisons contained in the exhaust prior to contact with the oxidation catalyst . the engine oil preferably has a very low ash content to minimize sulfur combustion components in the exhaust to reduce masking of the oxidation catalyst . the first volume preferably has a pressure relief valve set to relieve at a pressure greater than the maximum normal operating pressure of the engine to avoid excessive pressure excursions of the engine exhaust from damaging the oxidation catalyst .