The Cummins Westport ISL G and ISX12 G spark ignited natural gas engines use Stoichiometric combustion with cooled gas exhaust recirculation (EGR) and a Three-Way Catalyst (TWC). This technology was developed to meet the stringent 2010 EPA emission requirements and was introduced with the ISL G in June 2007.
The cooled-EGR system takes a measured quantity of exhaust gas and passes it through a cooler to reduce temperatures before mixing it with fuel and the incoming air charge to the cylinder. Stoichiometric combustion in combination with cooled-EGR creates the ideal combustion process with the chemically correct mixing of fuel and air, offering increased power density and thermal efficiency. It also reduces in-cylinder combustion temperatures and creates an oxygen-free exhaust, which then enables the use of a TWC for nitrogen oxide (NOx) control.