Combined Low and High Pressure EGR for Higher Brake Efficiency with Partially Premixed Combustion

Paper #:
  • 2017-01-2267

  • 2017-10-08
The concept of Partially Premixed Combustion (PPC) in engines has shown to achieve very high gross indicated efficiencies, but at the expense of gas exchange efficiencies. Most of the experimental research on PPC has been conducted on compression ignition engines designed to operate on diesel fuel and relatively high exhaust temperatures. The PPC concept on the other hand relies on dilution with high exhaust gas recirculation (EGR) rates to slow down the combustion which results in low exhaust temperatures, but also high mass flows over cylinder, valves, ports and manifolds. A careful design of the gas exchange system, EGR and charge air coolers is therefore of utter importance. Experiments were performed on a heavy-duty, compression ignition engine using a fuel consisting of 80 percent 89 RON gasoline and 20 percent n-heptane. A wide range of engine speeds and loads were run using a long route EGR system. The experiments served as a validation basis for a one-dimensional simulation model. Using the model, a comparison between long and short route EGR was performed. The results show that, at low gas exchange efficiencies, the short route EGR system showed higher brake thermal efficiencies than the long route EGR system. However, when the isentropic efficiency of the turbocharger was increased, the long route system performed better. The influence of EGR and charge air cooler outlet temperature on brake thermal efficiency and maximum load was also investigated. The conclusion is that by increasing the temperature from 20 °C to 80 °C, the maximum load attainable decreased with 30 percent and the brake thermal efficiencies was five percent lower on average. The highest influence was found when using the long route EGR system.
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