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Engine and Emissions Performance Calculator
Engine Parameter Monitoring System Guidelines developed in prior PRCI work has confirmed that five engine parameters govern engine emissions: 1) Speed, 2) Torque (fuel flow per stroke), 3) Air Manifold Pressure (AMP), 4) Air Manifold Temperature (AMT); and, 5) Ignition Timing.
Conventional methods of engine emissions mapping and modeling required the development of complex multi-dimensional thumbprints to characterize the effects of all five of these parameters. Calculation of the trapped equivalence ratio normalizes the effects of both AMP and torque, significantly reducing the degrees of freedom and resulting in a single parameter that primarily governs emissions. However, important secondary effects remain, particularly for NOX emissions including speed, AMT, and ignition timing.
The speed effects are particularly important for highly turbocharged engines operating over a wide range of AMP’s and airflows. The Guidelines recommended utilizing a multi-parameter linear combination of equivalence ratio, speed, AMT and IT (as required) when mapping or modeling emissions. While somewhat cumbersome, the approach was effective and is in use in engine control and PEMS applications.
Though certainly an improvement over previous approaches, the PRCI-GRI method still requires significant testing, most notably of, combustion airflows. In addition, the results still tend to be engine “make and model” if not unit specific, necessitating the comprehensive mapping of multiple units to develop the required database.
Many years of engine testing data and experience allowed standardized methods to document the methodology for modeling, calculating and validating engine and emissions. The performance data is based on the trapped equivalence ratio (Φ), or TER. As each major parameter contributes to the TER in some fashion, this makes the TER a possible output parameter of a theory-derived, empirically-confirmed computer-based calculation tool. This tool normalizes engine inputs for a given engine type, and processes enough independent operating parameters that a TER for the engine can be calculated. With the TER in hand for a given air and fuel flow configuration, engineers can determine how much additional air flow is needed to attain NOX targets, and specify a turbocharger upgrade or replacement accordingly. This tool has proven robust for both conventionally-fueled engines and enhanced mixing engines, and can save substantial amounts of time and money by avoiding incorrect turbochargers. It is available to PRCI members on the PRIME website for download and use.