Development of the Charge Air Integrated Manifold Engine Numerical (CAIMENS) for Active Air Control System Implementation
The development of a turbocharged engine system has allowed natural gas transmission companies to increase the air flow to the engine. This increased air flow has been strategically used to decrease pollutant emissions, such as NOX, to meet current emission regulations. In the future, regulations will be tightened, forcing transmission companies to look past turbochargers for compliance. The solution to further decreasing emissions lies not in further retrofit, but focusing on the physics of the current system. The physics of the manifold impedes equal distribution of air from the turbocharger to each cylinder. Imbalance in air flow creates a discontinuity in trapped equivalence ratio from cylinder to cylinder. Trapped equivalence ratio is directly proportional to NOX production and a function of the fuel flow rate, air flow rate, and, in a two-stroke cycle engine, the scavenging efficiency. Only when these three characteristics are balanced cylinder to cylinder will the combustion and the NOX production in each cylinder be equal. The engine NOX production will be disproportionately high if even one cylinder operates less lean relative to the other cylinders. This paper reports on an investigation into the transient, compressible flow physics that impact the trapped equivalence ratio. A comprehensive, variable geometry, multi-cylinder Turbocharger-Reciprocating Engine Computer Simulation (T-RECS) has been developed to illustrate the effect of airflow imbalance on an engine. A new model, the Charge Air Integrated Manifold Engine Numerical Simulation (CAIMENS), is a manifold flow model coupled with the T-RECS engine processor that uses an integrated set of fundamental principles to determine the crank angle-resolved pressure, temperature, burned and unburned mass fractions, and gas exchange rates for the cylinder. CAIMENS has the ability to show the transient impact of one cylinder firing on each successive cylinder. The pulsation model also describes the impact of ma
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