SI Engine Lean-Limit Extension Through LPG Throttle-Body Injection for Low CO2 and NOx 2006-01-0495
This paper presents the experimental results of a new look at throttle body injection (TBI) for LPG, targeting the same objectives as fourth generation LPG systems. The TBI system is configured from CFD studies to minimize cylinder-to-cylinder air-fuel variations, enabling the lean limit to be extended as far as lambda 1.6.
An in-line, six-cylinder engine with a compression ratio of 11.7:1 (up from the standard 9.65:1) over a range of speed/torque conditions was utilized, with the air/fuel ratio varied from lambda 1.2 to 1.6. Additionally, cylinder-to- cylinder air-fuel variations were measured over a range of speeds and throttle positions representing most of the steady state parts in the Euro drive-cycle for light-duty vehicles.
It is shown that mixing characteristics have a considerable effect on emissions and thermal efficiency. Comparisons of thermal efficiency and specific emissions of HC, NOx, CO2 and CO against liquid and gaseous phase LPG multipoint port injection (MPI) systems tested on the same engine show superior mixing of the throttle-body system. Notable improvements in emissions and thermal efficiencies were achieved when compared with original gasoline sequential port injection system. At lambda 1.6, NOx is low enough to meet Euro 4 standards without the need of a reducing catalyst. Best emissions observed for the TBI system were reductions of 74% for HC, 98% for NOx, 91% for CO, 40% for CO2 and a rise of 19% in thermal efficiency.