Jin-Wook Lee

Hydraulic Simulation and Experimental Analysis of Needle Response and Controlled Injection Rate Shape Characteristics in a Piezo-driven Diesel Injector

The More precise control of the multiple-injection is required in common-rail injection system of direct injection diesel engine to meet the low NOx emission and optimal PM filter system. The main parameter for obtaining the multiple-injections is the mechanism controlling the injector needle energizing and movement. In this study, a piezo-driven diesel injector, as a new method driven by piezoelectric energy, has been applied with a purpose to develop the analysis model of the piezo actuator to predict the dynamics characteristics of the hydraulic component (injector) by using the AMESim code and to evaluate the effect of this control capability on spray formation processes. Aimed at simulating the hydraulic behavior of the piezo-driven injector, the circuit model has been developed and verified by comparison with the experimental results. We found that the input voltage exerted on piezo stack is the dominant factor which affects on the initial needle behavior of piezodriven injector than the hydraulic force generated by the constant injection pressure. And the piezo-driven injector has more degrees of freedom in controlling the injection rate with the high pressure than a solenoid-driven injector. The piezo-electric characteristics of a piezodriven diesel injector, which was manufactured as prototype version was experimentally examined to confirm the injection driving principle based on the inverse piezo-electric effect and to ensure the operating performance of a prototype piezo-driven injector. The injection duration is proportional to the external input pulse duration for driving the piezo-driven injector. The higher the output current (voltage) applied to piezodriven injectors controller, the longer the hold time on the injection duration is. The charging time decreases rapidly as the output current increase. And the needle’s response of a piezo-driven injector by using an accelerometer has been investigated together with the evaluation of the injection rate employing Bosch’s method. Results were compared between a conventional solenoid-driven injector and the piezodriven injector, both equipped with the same micro-sac multi-hole injection nozzle. The experimental results show that the piezo-driven injector has a higher injection flow rate by a fast needle response time and it is possible to control the injection rate slope by altering the induced current. Also these experimental results showed favorable agreement with the predicted simulation results by AMESim environment.

Effects of needle response on spray characteristics in high pressure injector driven by piezo actuator for common-rail injection system

The common-rail injection systems, as a new diesel injection system for passenger car, have more degrees of freedom in controlling both the injection timing and injection rate with the high pressure. In this study, a piezo-driven injector was applied to a high pressure common-rail type fuel injection system for the control capability of the high pressure injector’s needle and firstly examined the piezo-electric characteristics of a piezo-driven injector. Also in order to analyze the effect of injector’s needle response driven by different driving method on the injection, we investigated the diesel spray characteristics in a constant volume chamber pressurized by nitrogen gas for two injectors, a solenoid-driven injector and a piezo-driven injector, both equipped with the same injection nozzle with sac type and 5-injection hole. The experimental method for spray visualization was based on back-light photography technique by utilizing a high speed framing camera. The macroscopic spray propagation was geometrically measured and characterized in term of the spray tip penetration, spray cone angle and spray tip speed. For the evaluation of the needle response of the above two injectors, we indirectly estimated the needle’s behavior with an accelerometer and injection rate measurement employing Bosch’s method was conducted. The experimental results show that the spray tip penetrations of piezodriven injector were longer, on the whole, than that of the solenoid-driven injector. Besides we found that the piezo-driven injector have a higher injection flow rate by a fast needle response and it was possible to control the injection rate slope in piezo-driven injector by altering the induced current.

Trajectory Generation for Rendezvous of Unmanned Aerial Vehicles with Kinematic Constraints

In this paper, we present an efficient method for finding collision-free trajectory for multiple unmanned aerial vehicles (UAVs) with kinematic constraints and for their rendezvous to form a formation. First, we construct a visibility graph that supports a minimum turning radius constraint when constructing the graph, so that additional smoothing process is not necessary. Second, we modify the standard A* to consider velocity conditions for rendezvous and collision avoidance with obstacles or other UAVs. Permitting velocity decrease only when it is required that the robot slow down the speed, unnecessary node expansions are avoided. This multi-vehicle problem is solved in a decoupled manner. In order to show the effectiveness of this approach, we present simulation results of rendezvous and independent flight for multiple UAVs.

The Effects of Tumble Flow on Lean Burn Characteristics in a Four-Valve SI Engine

The authors would like to acknowledge the financial support provided for this project by the Korean Goverment, through the scheme of the National G7 Project. They would also like to Mr J.H. Lee for his contribution to the experiments

Study of Supersonic Flame Acceleration within AN-based High Explosive Containing Various Gap Materials

We study the gap effect on detonating high explosives using numerical simulation. The characteristic acoustic impedance theory is applied to understand the reflection and transmission phenomena associated with gap test of high explosives and solid propellants. A block of charge with embedded multiple gaps is detonated at one end to understand the ensuing detonation propagation through pores and non uniformity of the tested material. A high-order multimaterial simulation provides a meaningful insight into how material interface dynamics affect the ignition response of energetic materials under a shock loading.

A Study on the Characteristics of Swirl Flow in Transparent Engine with Different Swirl Ratio and Piston Configuration for Heavy-duty LPG Engine

The configuration of intake port and piston is a dominant factor of inlet air flow and mixture formation in an engine cylinder, resepectively. This study has analyzed intake port and piston characteristics for swirl flow of a heavy-duty LPG engine. As an available technology to optimize intake port, the steady flow rig test has been applied for measuring swirl ratio and mean flow coefficient. And we measured the mean velocity and turbulence intensity of swirl flow under motoring condition in transparent engine cylinder by backward scattering LDV system. From these results, the piston and cylinder head with a good evaluated swirl flow characteristics were developed and adapted fur a 11L heavy-duty engine using the liquid phase LPG injection (LPLI) system. The obtained results are expected to be a fundamental data for developing intake port and piston.