Turbochargers for natural gas engines have evolved significantly, driven by stringent emissions regulations and the adoption of stoichiometric burning.
Modern natural gas turbochargers feature distinct components compared to their diesel counterparts. A decade ago, turbochargers for natural gas and diesel engines were not very different. However, new emissions regulations have driven the development of turbochargers specifically designed for natural gas engines. These turbochargers are adapted to stoichiometric burn conditions, where the mix of oxygen and fuel is precisely balanced. This balance ensures efficient combustion, leaving no unburnt fuel or excess oxygen.
Turbochargers developed for modern natural gas engines, have unique components like a dual wastegate port, larger actuators and a material housing made of composite materials that can withstand the higher temperatures a stoichiometric burn requires.
Turbochargers for natural gas engines are distinct from those used in diesel engines due to the unique demands of natural gas combustion like higher operating temperatures and distinct air-to-fuel ratios. Unlike diesel engines, which operate with a lean burn and a higher air-to-fuel ratio, natural gas engines require a stoichiometric burn. This means the mixture of oxygen and fuel is balanced precisely (1:1 air-to-fuel ratio) for efficient combustion, ensuring no unburnt fuel or excess oxygen remains. Consequently, natural gas engines require smaller turbochargers since less air is needed for stoichiometric combustion compared to the leaner burn in diesel engines. For example, a diesel engine might need an HE500 turbo, but a natural gas engine could use an HE300 or HE400 due to its lower air requirements.
Achieving this efficient combustion has led to significant modifications in many system components, including the incorporation of a dual wastegate port to handle the high bypass capability necessary for natural gas turbochargers. This port regulates exhaust flow, controls pressure and prevents over-boost.
The intense temperatures and pressures of natural gas engines also influence turbocharger design. While diesel engines prioritize turbocharger efficiency, natural gas engines focus on achieving the required mass flow rate and meeting exhaust gas recirculation (EGR) demands. As a result, turbochargers for natural gas engines are built with high-temperature materials, particularly at the turbine stage, to resist thermal fatigue.
These turbochargers also require water-cooled bearing housings to manage the elevated temperatures, necessitating additional piping and connections to maintain coolant flow.
While natural gas engines share many components with their diesel counterparts, key modifications have been made to turbochargers to accommodate the use of gaseous fuel. These changes address the higher temperatures and different flow characteristics unique to natural gas, ensuring optimal performance and durability.
A decade ago, natural gas and diesel turbos were nearly identical, but stringent emissions regulations like Euro 6 and EPA standards have driven significant changes, including the shift to stoichiometric burning, which increased operating temperatures and created the need for new turbocharger configurations.
By shifting to stoichiometric burning, Cummins was able to reduce the need for aftertreatment systems like Diesel Oxidation Catalysts (DOCs) or Selective Catalytic Reduction (SCR) systems, which ultimately lowered the cost of the engines and turbos. Source