An Exploratory Look at an Aggressive Miller Cycle for High BMEP Heavy-Duty Diesel Engines 2019-01-0231
Through aggressive application of the Miller Cycle, using two-stage turbocharging, medium speed diesel marine and stationary power engines are demonstrating over 30 bar BMEP, and over 50 percent thermal efficiency. The objective of this work was to use engine cycle simulation to assess the degree to which the aggressive application of the Miller Cycle could be scaled to displacements and speeds more typical of medium and heavy truck engines. A 9.2 liter six-cylinder diesel engine was modeled. Without increasing the peak cylinder pressure, improved efficiency and increased BMEP was demonstrated. The level of improvement was highly dependent on turbocharger efficiency – perhaps the most difficult parameter to scale from the larger engines.
At 1600 rpm, and a combined turbocharger efficiency of 61 percent, the baseline BMEP of 24 bar was increased to over 26 bar, with a two percent fuel consumption improvement. As turbocharger combined efficiency increased, to over 75 percent as seen in large, medium speed engines, over 29 bar BMEP was achieved, with over six percent fuel consumption improvement. Application considerations including speed and load range, and emission constraints are discussed.