Kyung-Hwan Lee

An Investigation of the Effect of Changes in Engine Operating Conditions on Ignition in an HCCI Engine

The dependence of the ignition timing in an HCCI engine on intake temperature and pressure, equivalence ratio, and fuel species is investigated with a zero-dimensional model combined with a detailed chemical kinetics. The accuracy of the model is evaluated by comparing measured and computed results in a propane-fueled HCCI engine. It is shown that the peak pressure values are reproduced within 10% and ignition timing within 5° CA. The heat loss through the walls is found to affect significantly on the ignition timing for different inlet conditions. It is also shown that for the propane-fueled engine, the tolerance in intake temperatures is 20–25K and the tolerance in intake pressure is about 1 bar for stable operation without misfire or too early ignition. Comparison of propane and heptane fuels indicates that the tendency to misfire when heptane is employed as the fuel is less than that when propane is employed with the same wall temperature conditions. However, the heptane-fueled engine may have a Lower compression ratio to avoid too early ignition and hence lower efficiency. For the selected set of engine parameters, stable operations might be achieved for the heptane-fueled engine with twice as much tolerance in intake temperatures as for the propane-fueled engine.

Force/torque sensorless impedance control for indirect driven robot-aided gait rehabilitation system

Robot gait rehabilitation has been emerging as an important training technique for patients whose ability to walk is impaired. The “patient-cooperative” approaches are able to detect patients voluntary efforts and allow patients to actively influence a gait pattern during rehabilitation processes. The impedance control method is a key technique of “patient-cooperative” strategies that allows deviating desired trajectories by sensing interaction torque. This paper introduces an indirect drive gait training rehabilitation robot system which composed of timing belt and harmonic drive transmissions. We present compensation methods and investigate reaction torque observer (ROB) for estimating patient/robot interaction torque and its application in force/torque sensorless impedance control of patient-cooperative strategy in gait rehabilitation.

Development of engine speed control system for power supply of the robot

JINPOONG, a walking robot using hydraulic pressure, requires a power source to operate the power-pack. Therefore, power was supplied to JINPOONG by using an engine that has high power per unit engine weight. Hydraulic pump requires a constant rotating speed in order to supply stable hydraulic pressure because the pressure and flow rate changes according to rotating speed. This study proposes a way to maintain relatively stable rotating speed of engine with irregular and fluctuating load.

Preliminary results of force/torque sensorless impedance control for Walkbot

Robotic gait rehabilitation has been captured considerable attentions as an important training technique for walking impaired patients over the past few decades. In this paper, we successfully applied an impedance control for patient-cooperative strategy of gait rehabilitation without force/torque sensors for a commercial gait rehabilitation orthosis. The control method utilizes reaction torque observer (ROB) for estimating patient-robot interaction torque. Experiments were performed on five healthy subjects are given to demonstrate the feasibility of the applied method.

Numerical analysis on Distributions of Temperature and Flow Velocity in an Inertance Pulse Tube Cryocooler

The inertance pulse tube cryocooler (IPTC) is well known as one of the most effective cryocooler for the cooling of infrared imaging detectors and superconducting technologies. The reciprocating flow in an IPTC was modeled with a computational thermal fluid dynamics. Two dimensional modeling consists of the flows in the cylinder of compressor, a regenerator, a pulse tube, heat exchangers, an inertance tube, and a gas reservoir. The user-defined function was applied to the compression and expansion stroke of piston in the compressor. It was confirmed that the temperature at the cold heat exchanger decayed to the lowest temperature with an oscillating convergence due to the compression and expansion of piston in the compressor. The spatial distributions of temperature and flow velocity are also compared for the piston at the top dead center and bottom dead center during compression and expansion strokes.

Design and implementation of electronic governor system for 2 stroke engine

JINPOONG, a walking robot using hydraulic pressure, requires a power source to operate the power-pack. Therefore, power was supplied to JINPOONG by using an engine that has high power per unit engine weight. Hydraulic pump requires a constant rotating speed in order to supply stable hydraulic pressure because the pressure and flow rate changes according to rotating speed. This study proposes a way to maintain relatively stable rotating speed of engine with irregular and fluctuating load.

Cycle Resolved NO Emissions and Its Relation with Combustion Chamber Pressure in an S.I. Engine with Fast Response NO Analyzer

A fast response NO analyzer was applied to investigate the relation between cycle-by-cycle NO emissions and combustion chamber pressure. NO emissions were sampled at an isolated exhaust manifold of 4-stroke spark ignition engine to avoid the interference of exhaust gas from other cylinders. The linear correlation analysis was performed with collected data of NO emissions and combustion chamber pressure with respect to the various air-fuel mixture ratios and engine loads. The sampled data sets were obtained during 200 cycles at each operating condition. The results showed that there was a typical pattern in NO emissions from an exhaust port through a cycle. It was possible to set a block of crank angle in which the linear correlation coefficient between NO emissions and combustion chamber pressure was high. As the engine load increased, NO emissions were more dependent on combustion chamber pressure after TDC. It was also analyzed that the correlation between two parameters with respect to air-fuel mixture ratio tended to increase as mixture went leaner. Furthermore, this correlation coefficient for the mixture near the lean limit seemed to be kept high even though combustion was unstable.