Numerical Study of Effects of High Exhaust Gas Recirculation and Energy Recovery System on Diesel Engine Performance

摘要

This study investigates how high levels of exhaust gas recirculation (EGR) combined with certain fuel injection strategies and energy recovery systems affect diesel engine emissions and fuel economy. The key test apparatus was a John Deere 4.5L diesel engine which was modeled using the computer-based engine simulation tool GT-Power.The conclusion was made that utilization of high EGR levels (30% and above) can enable a diesel engine operating at low-load/low-speed conditions to meet Tier 4 emissions regulations without the use of NOx after-treatment, but that employment of such EGR levels will likely make necessary the use of soot after-treatment. Results found that using a single, late injection produced the lowest brake specific fuel consumption (BSFC) for high EGR operation conditions. Results also found that, among varying EGR levels and injection strategies tested, the combination of 30% or more EGR with a double injection produced the lowest levels for NOx and soot emissions combined, but at the cost of increased BSFC.This study also performed a numerical analysis on certain designs of energy recovery systems used to generate mechanical power from exhaust gas heat. Two Brayton cycle systems were tested, but a Rankine cycle system, also tested, proved to generate more power. A numerical study was performed on this Rankine cycle energy recovery system integrated into the John Deere engine, in which this engine was operated with 30% EGR, varying load/speed conditions, and either a low or high pressure EGR loop. It was found that for low-load/low-speed and high-load/low-speed operation conditions the Rankine cycle recovery system could decrease engine BSFC by 4% to 5%.