Study of Cylinder Charge Control for Enabling Low Temperature Combustion in Diesel Engines

Abstract

Suitable cylinder charge preparation is deemed critical for the attainment of a highly ho mogeneous, diluted, and lean cylinder charge, which is shown to lower the flame temper ature. The resultant low temperature combustion (LTC) can simultaneously reduce the NOx and soot emissions from diesel engines. This requires sophisticated coordination of multiple control systems for controlling the intake boost, exhaust gas recirculation (EGR), and fueling events. Additionally, the cylinder charge modulation becomes more complicated in the novel combustion concepts that apply port injection of low reactivity alcohol fuels to replace the diesel fuel partially or entirely. In this work, experiments have been conducted on a single cylinder research engine with diesel and ethanol fuels. The test platform is capable of independently controlling the intake boost, EGR rates, and fueling events. Effects of these control variables are evaluated with diesel direct injection and a combination of diesel direct injection and ethanol port injection. Data analyses are performed to establish the control requirements for stable operation at dif ferent engine load levels with the use of one or two fuels. The sensitivity of the combus tion modes is thereby analyzed with regard to the boost, EGR, fuel types, and fueling strategies. Zero-dimensional cycle simulations have been conducted in parallel with the experiments to evaluate the operating requirements and operation zones of the LTC com bustion modes. Correlations are generated between air-fuel ratio (A), EGR rate, boost level, in-cylinder oxygen concentration, and load level using the experimental data and simulation results. Development of a real-time boost-EGR set-point determination to sus tain the LTC mode at the varying engine load levels and fueling strategies is proposed.

Tutorial of model-based powertrain and aftertreatment system control design and implementation

“…Particularly in clean Low Temperature Combustion (LTC) cycles, significant charge dilution is achieved through EGR and concurrent increase of intake boost is necessary for increasing engine power density. Thus, control of the turbocharging and EGR interaction is critical for stable operation in LTC mode [6]. A significant amount of work has been done on the characterization and coordinated control of variable geometry turbocharging (VGT) and EGR for conventional diesel engines [7].…”

“…The gas species concentration would change due to chemical reaction and gas exchange processes which happened between the cylinder and the manifolds and is described using (4). The mass and energy balances of the engine cylinder are described using (5) and (6). The combustion process is considered to take place close to the top dead center of the cylinder and is approximated as constant volume combustion which bears a two-step reaction mechanism which is expressed by three-parameter Arrhenius functional form in (7).…”

An engine cycle analysis of diesel-ignited ethanol low-temperature combustion

“…An example of an ethanol evaporation scheme is shown in Figure 22. Further details of the modelling approach may be found in the previous publication by Divekar et al 46…”