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In this study, SCR system is employed to selectively reduce NOX that is a major cause of environmental pollution from diesel engines. In particular, this paper focuses on urea injection strategies dependent on NO/ NOX ratio. An injection control algorithm is developed based on the chemical ratio between the amount of engine out NOX data obtained from Engine Management System (EMS) and the amount of NH3. Therefore, in order to decide the amount of injection quantity, the NO/NOX ratio from the engine out NOX should be considered in order to minimize NH3 slip while maximizing NOX reduction. Experiments are conducted with a 2.2-liter diesel engine for passenger vehicles with Diesel Oxidation Catalyst (DOC) and Diesel Particle Filter (DPF). Real time control, using Pulse Width Modulation (PWM) duty ratio for dosing module and supply module, is performed by real time computer with its injection control algorithm developed in the Matlab Simulink environment.

Recent research has focused on engine combustion technology as well as application of after-treatment in order to comply with emission regulation. However, it is much more efficient way to control emissions from engine itself and furthermore research on engine control will provide the direction of after-treatment technology in future. Furthermore, emission standard regulation for passenger diesel vehicles has been stringent compared to others and nano-particles will be included in EURO6 regulation in Europe and similar emission standard will be introduced in Korea. A 3.0-liter high-speed diesel engine equipped with by CRDI system of 160 MPa injection pressure, and an intake/exhaust system of V type 6-cylinder turbo-intercooler was applied. The conditions of fuel spray and combustion were investigated by setting up an ETAS system which is a similar condition to the engine dynamometer test.

This research aims to obtain fundamentals regarding overall combustion characteristics of pre-mixed and direct injected type CNG fuel inside a constant volume chamber. A visualization technique was introduced to a constant volume chamber in order to investigate combustion and emission characteristics of premixed and direct injected type CNG fuel inside a constant volume chamber. The experiment on a premixed combustion was conducted by measuring constant pressure and emission and controlling speeds of a swirling motor and equivalence ratios in order to investigate swirling effects on flame propagation. Faster combustion speed and higher combustion pressure were occurred in a direct injected type combustion even under the lean condition of the equivalence ratio 0.6 compared to premixed combustion.

Steady flow bench test is a practical, powerful and widely used one for most engine manufacturers to give a design concept of a new engine, especially for the intake system. In order to use the steady data as a performance index, it is necessary to build up massive database, which can correlate the port characteristics with engine data. However, it is hard to investigate all port and valve shapes with experimental tools. The steady flow scheme is relatively simple and its results are bulk ones such as flow rates and momentum of flow. Therefore, computational simulation can easily be applied for evaluation of the intake port and valve designs. In this study, three-dimensional numerical analysis of the steady flow characteristics was performed on intake valve design for comparison with experimental data, which can confirm the feasibility of applying analytic method. For this purpose, the effect of valve curvature on flow rate was estimated using a CFD code.

Electromagnetic valve (EMV) actuation system is a new technology for the improvement of fuel efficiency and the reduction of emissions in SI engines. It can provide more flexibility in valve event control compared to conventional variable valve actuation devices. However, a more powerful and efficient actuator design is needed for this technology to be applied in mass production engines. This paper presents the effects of design and operating parameters on the thermal, static and dynamic performances of the actuator. The finite element method (FEM) and computer simulation models are used in predicting the solenoid forces, dynamic characteristics and thermal characteristics of the actuator. Effect of design parameters and operating environment on the actuator performance were verified before making prototypes using the analytical models. To verify the accuracy of the simulation model, experimental study is also carried out on a prototype actuator.

UEGI(Unburned Exhaust Gas Ignition) is expected to help faster warm-up of a close-coupled catalytic converter (CCC) by igniting the unburned exhaust mixture using two glow plugs installed upstream of the catalyst. In this study, a control module and an algorithm for the UEGI technology was developed. In addition, a hydrocarbon adsorber was tested with the UEGI system for more effective reduction of HC emission during the cold start. The control module changes I/O signals of the ECU, to control ignition on/off, glow plug on/off, and A/F ratios during cold start. Because the system is designed to be applicable to conventional vehicles, its repeatability, stability, and precision of control were tested and analyzed on an engine test bench and vehicle test. Experimental results show that the CCC reaches the light-off temperature faster compared with the baseline exhaust system. Therefore HC and CO emissions are reduced significantly during the cold start.

Recent stringent emission regulations need fast light-off of catalysts to reduce HC and CO emissions during cold start. Cranking Exhaust Gas Ignition (CEGI) system, developed in this study, cuts off the ignition signals for 10 seconds during the cranking period for the unburned mixture to bypass the combustion chamber and flow through the exhaust manifold. When the unburned mixture reaches two glowplugs mounted upstream of the catalyst, it is ignited and releases thermal energy to warmup the catalyst. Results from the vehicle tests showed that the catalyst reaches the light-off temperature within 20 seconds and the reduction of exhaust emission was 47.7% for THC and 88.6% for CO in the cold-transient phase of the FTP-75 mode.

The Fuel stratification process has been investigated in the cylinder of an axially stratified lean burn engine by visualizing fuel behavior. Planar laser light sheet from an Nd:YAG laser has been illuminated through the transparent quartz cylinder of a single cylinder optical engine. Mie scattered light has been captured through the quartz window in the piston head with an ICCD camera. Fuel has been replaced with an ethanol droplets to utilize an atomized fuel spray for visualization purposes. Swirl ratios have been varied by changing cylinder heads with different swirl numbers and injection time has been varied to find the effect of fuel stratification. A higher lean mixture limit was achieved when the fuel remained at the combustion chamber as stratified with the proper combination of fuel injection timing swirl flow.

The mechanism of axial stratification was investigated in a port injection SI engine. The port swirl and tumble number characterized the ports. The experiment consisted of a steady flow rig test for defining flow characteristics, engine test for finding lean misfire limit, fuel behavior tracing in a steady flow rig for the understanding basic stratification, fuel motion visualization in motored engine for the investigating real stratification process and flame capturing under known stratified conditions. The results show that not only swirl but also tumble affects axial stratification with the interaction of injection timing. It was also observed that stable initial flame improved engine stability by stratification, but the flame propagation pattern and direction was not affected by stratified condition, load, air-fuel ratio and fuel phase but by bulk in-cylinder flow pattern.

Results from an experimental study of flow distribution in a close-coupled catalytic converter (CCC) are presented. The experiments were carried out with a flow measurement system specially designed for this study under steady and transient flow conditions. Flow distribution at the exit of the first monolith was measured by a pitot tube. Numerical analysis was also performed for comparison. Experimental results showed that the flow uniformity index decreases as Reynolds number for the flow increases. For steady flow conditions, the flow through each exhaust pipe concentrates on a specific region of the monolith. The transient test results showed that the flow through each exhaust pipe, in the engine firing order, interacts with each other to make the flow distribution uniform. The numerical analysis results supported the experimental results, and helped explain the flow distribution in the CCC.

An experimental study was carried out to develop a new knock-detection method using cylinder pressure, block vibration and sound pressure signals from a spark-ignition (SI) engine. As a first step for knock detection, the 1st, 2nd and 3rd harmonic knock frequencies were determined by analyzing the cylinder pressure signals under a wide range of engine operating conditions. Since these knock frequencies were found to be independent of engine operating conditions and the standard deviations of these knock frequencies were small, three narrow band-pass filters were designed and applied to process the raw signals from the engine. Then a new method, called the Sum of Divided Band-Pass (SDBP) filtering method, was proposed to determine knock intensity, and it was shown to be better than the other methods in terms of knock detection sensitivity and background noise removal. Knock intensity greatly varies with engine operating conditions, knock sensor locations and fuel characteristics, etc.

A computer code named ESTAP (Exhaust System Thermal Analysis Program), capable of running in IBM-PC compatibles, was developed to reduce the time and cost of exhaust system optimization. ESTAP solves one-dimensional transient heat transfer problems of exhaust systems. It can predict the surface temperature of exhaust pipes and the exhaust gas temperature at the inlet of an underbody catalytic converter during the first 200 seconds of FTP-75 test. Results showed that the exhaust gas temperature can be accurately predicted, and ESTAP is an effective tool to optimize exhaust systems.