TDC Position Research Articles

Numerical and experimental investigation of the flow structure in a diesel engine with different piston bowl structure

In this study, unfired (cold) flow application was investigated in a single cylinder die-sel engine with different combustion chamber geometries. In the experimental study, images obtained with the help of an endoscopic camera for different cycle points were instantly detected at constant speed. At the same time, velocity distributions of two dif-ferent combustion chambers for different crank angles were analyzed in Ansys Forte software at before and after TDC. Thus, the flow distributions of different combustion chamber geometries in the chamber were compared. It can be said that regional swirl is formed in the newly developed combustion chamber geometry and develop in the chamber rather than the piston base compared to the standard combustion chamber. In addition, especially during the compression process, the squish movement of the bowl was observed with the movement of the piston. Here, it could be said that the newly de-veloped chamber geometry is more effective than the standard bowl geometry. When the distribution of velocity vectors in the x-y and x-z axis were examined in numerical analysis, especially in the TDC position, it was determined that the interaction of the flow developed by the new bowl geometry with the fuel droplets was more evident. While it is seen that the vector velocity changes are close to each other at the 6920 CA before the fuel injection, it is seen that higher flow velocities are formed for the standard combustion chamber at the 7200 CA where the spraying continues and develops.

Piston motion control for a dual free piston linear generator: predictive-fuzzy logic control approach

The free-piston engine has a lot of potential to alter the conventional combustion engine due to mechanical structural simplicity, high engine efficiency, reducing hazardous gas emission and fuel flexible combustion. However, accuracy of piston motion control is a major challenge in all types of free-piston engine as well a dual free piston engine generator (DFPG) because of not having a crankshaft mechanism. This article describes a simulation investigation of a predictive-fuzzy logic control method conducted on the DFPG prototype in University of Ulsan. First, the simulation model of the DFPG consisted of a free-piston engine and a linear alternator is established and running in Matlab/Simulink environment. Then simulation result is validated against experimental data to prove validity of the simulation model. Second, a predictive-fuzzy logic (PFL) control method is proposed to apply to the DFPG and its performance is carried out using the full-cycle simulation model. The PFL strategy is demonstrated to improve the DFPG performance and more effective than the PID one in terms of settling time, TDC error, and cycle-to-cycle variation. According to results, the PFL controller reduces settling time 30 % in comparison to PID controller. The PFL controller has also 0.52 mm better TDC position error than the PID controller is 0.76 mm. Coefficient of variation values is found to be 1.0 %, and 1.9 % for the PFL controller and PID controller, respectively. This means that the PFL controller is a powerful method to dampen cycle to cycle variations in the DFPG.

Wear study and EHD lubrication analysis on connecting rod big end bearings of off‐highway application engine

AbstractThe connecting rod big end bearings are under dynamic lubrication during working cycle, and in most of the time, the con rod is subjected to compressive stress. The conventional method of performing an EHL analysis on a bearing involves development of complex mathematical equations and simplification of actual physical model. This paper presents a methodology to model and simulate the elastohydrodynamic lubrication and wear study of connecting rod big end bearings of off‐highway application engine using the application of computational fluid dynamics (CFD) and computational structural dynamics (CSD) approaches. The pressure field for a full journal bearing operating under laminar flow regime with various eccentricities was obtained by CFD, and fluid pressure distribution and deformation in the bearing liner due to pressure were evaluated using FSI approach. Relevant parameters of lubrication characteristics were analyzed to optimize the eccentricity value. The maximum bearing load value of 21 kN was noticed at TDC position for the optimum eccentricity. The load distribution indicated critical points in the bearing, and the data obtained from bearing load and sliding velocity of journal were used in Archard's wear relation to determine the wear depth along the bearing width. The simulated wear results were compared with three‐cylinder off‐highway application engine con rod big end bearings, which ran for 1000 hours at full load condition, and satisfactory agreement was observed between experiment and simulation values.

Study of Top Dead Center Measurement and Correction Method in a Diesel Engine

The thermal loss angle error analysis and maximum pressure determination method analysis were conducted first. Then the polytropic exponent method, the inflection point analysis, the loss function method and the symmetry method were utilized under different rotating speed, load and cooling water temperature, to calculate TDC in D6114 diesel engine and the results were compared with TDC position measured under the same condition with direct method of measurement. The study proved that (1) thermal loss angle of the diesel engine ranges from -1.0 ~ -0.6°CA; (2) Thermal loss angle is mainly affected by rotating speed and is reducing when rotate speed increases;(3) the symmetry method is generally the optimum for calculating the thermal loss angle of automotive diesel engines, with an error within 0.2°CA.

선박용 디젤엔진의 출력산정에 관한 연구

Abstract: To obtain the engine output correctly is basically very important factor for estimating a engineperformance. But, it has been reported that the IHP measured from electronic indicator such as MIPS(MeanIndication Pressure System) has a deviation compared to mechanical indicator. It was reported by authors that the uncertainty of crank angle for TDC position could be one of the reasons. In this paper, the uncertainty of crank angle for TDC position and its influence to engine output were investigated respectively about M/E and G/E for marine diesel engines. For the purpose, two sampling methods of pressure in cylinder were considered which were 'angle base sampling' and 'time base sampling'. Angle basesampling is real crank angle acquired from angle encoder which is attached to crank shaft and time base sampling is crank angle calculated by detected revolution with Z-pluse of encoder. Time base sampling issame method of MIPS. This paper concluded that time base sampling method is not suitable for obtainingthe output of marine diesel engine on board because oftion and load fluctuation. instantaneous speed variaAlso it is verified that the variation of engine speed by load fluctuation should be one of reasons additionally in case of M/E.

非燃焼時のシリンダ内圧力を用いたTDC位置の正確な決定法について

A wrong TDC position leads to incorrect cylinder pressure-crank angle phasing, and has been recognized as a major source of error in thermodynamic calculation results such as indicated mean effective pressure, heat release rate, or thermal and mechanical efficiencies. One of the most convenient ways to determine TDC is to use measured cylinder pressure obtained from a pressure transducer under non-firing conditions. However, it is impossible to determine TDC precisely because the thermodynamic loss angle is unknown. In the paper a new method for TDC determination based on a measured non-fired cylinder pressure versus time diagram has been presented. In this method there is no need to know the details of the heat transfer formula, heat transfer coefficients or the properties of working gas in the engine . The method is applied to a four stroke high-speed marine diesel engine successfully. This method is distinguished for its high accuracy and is also probably applicable to large two stroke diesel engines.

저속박용디젤기관의 순간회전속도 변동에 관한 연구

The variation of the crankshaft speed in a multi-cylinder engine is determined by the resultant gas pressure torque and the torsional deformation of the crankshaft. Under steady state operation, the crankshaft speed has a quasi-periodic variation. For the diagnosis the engine instantaneous speed versus crankshaft angle is utilized. This paper describes a simple measurement method of the engine instantaneous speed versus crankshaft angle using the teeth on the flywheel of the crankshaft. Two non-contacting magnetic pickup combinations detect the crank angle and TDC position for the data acquisition. The results from experiments on a 6 cylinder marine diesel engine demonstrate that the crankshaft speed variation are detected with good resolution. And the crankshaft speed variation is investigated according to the operation conditions. Also, it is confirmed that the engine output measured by EMS can be evaluated larger than the actual value due to TDC position error caused by instantaneous speed variation.