汽车外文翻译半机电性气门在一台单缸火花点火发动机排放影响.doc

Effect of a semi electro-mechanical engine valve on performanceand emissions in a single cylinder spark ignited engine(Department of Automotive Education, Karabuk University, Karabuk 78050, Turkey)E-mail: ozdalyan; dogan_oguzhanyahoo.co.ukReceived Feb. 25, 2009; Revision accepted July 7, 2009; Crosschecked Nov. 8, 2009Abstract: In this study, an electro-mechanical valve (EMV) system for the intake valve of a four stroke, single cylinder, overhead valve and spark ignition (SI) engine was designed and constructed. An engine with the EMV system and a standard engine were tested to observe the effects of the EMV on engine performance and emissions at different speeds under full load. The EMV engine showed improved engine power, engine torque and break specific fuel consumption (BSFC). A 66% decrease in CO emissions was also obtained with the EMV system, but hydrocarbons (HC) and NOx emissions increased by 12% and 13% respectively. Key words: Semi electro-mechanic, Camless engine, Electro-mechanic engine valve, Engine performance, Emissions doi:10.1631/jzus.A0900119 Document code: A CLC number: TH131.Introduction All internal combustion engines (ICE) have mechanically actuated systems for opening intake and exhaust valves. Traditional valve systems have con-stant valve timing which restricts engine performance especially at low and at high engine speeds. Control-ling valve operation in ICEs effective method for improving engine performance and emissions over a range of engine speeds. Parameters such as cam shape, valve timing, valve opening duration and valve lifting have a major impact on engine performance and emissions (Barkan and Dresner, 1989; Krauter et al., 1992; Hatano et al., 1993; Cinar, 1998; Akba, 2000; Pischinger et al., 2000; Stein et al., 1995). To increase torque and reduce fuel consumption in gasoline engines, manufacturers are increasingly using variable valve timing systems in production engines. Most valve timing systems used for improving engine performance are dependent on the camshaft. The mechanical variable valve timing systems are complex but greatly reduce the limitations of traditional valve systems, especially in regard to volumetric efficiency (Barkan and Dresner, 1989). However, except for BMWs Valvetronic system, they cannot control all parameters such as valve timing, valve lifting and valve opening duration simultane-ously, continuously and completely independently. Lotus Engineering has developed research and production versions of their fully variable valve system that are not dependent on camshafts. The Lotus system can also independently control valve timing, valve lifting and the duration of valve opening. The power and torque increase obtained by using variable intake valve timing is between 5% and 21% The improvement in fuel consumption obtained by variable intake valve timing is between 6% and 30% (Ahmad and Theobald, 1989; Barkan and Dresner, 1989; Dresner and Barkan, 1989; Asmus, 1991; Demmelbauer et al., 1991; Gould et al., 1991; Hatano et al., 1993; Urata et al., 1993; Lee et al., 1995; Levin and Schlecter, 1996; Moriya et al., 1996; Pischinger et al., 2000). The improvement in CO emissions obtained using variable intake valve timing is between 5% and 60% (Dresner and Barkan, 1989; Gould et al., 1991; Lee et al., 1995; Moriya et al., 1996). In some studies, hydrocarbon (HC) emissions were shown to increase with the use of variable valve timing (e.g., Lee et al., 1995). Other studies showed that HC emissions were reduced by between 4% and 40% (Dresner and Barkan, 1989; Gould et al., 1991; Lancefield et al., 1993; Moriya et al., 1996). Nox emissions were reported to decrease by from 30% to 90% (Dresner and Barkan, 1989; Gould et al., 1991; Lee et al., 1995; Moriya et al., 1996). The opening speed of the valve increases the volumetric efficiency of the engine and the reduction in valve lifting decreases the friction arising in the valves (Levin and Schlecter, 1996). With a variable valve timing system employing the EMV system, all relevant parameters can be controlled simultaneously and completely independently. Therefore, in addition to improvements in fuel economy and emissions, engine performance is greatly improved (Levin and Schlecter, 1996; Pischinger et al., 2000). The variable valve timing system, which is a completely electro-mechanical system, does not need a camshaft and therefore enables the production of a camless engine. A semi electro-mechanical camless engine is one in which only intake or only exhaust valves are driven electro-mechanically. Camless engine systems have a great potential as they have the advantages of a mechanically working variable valve timing system and because the control of valve performance parameters is easier. There is a considerable collection of literature on camless engines. Recent studies have focussed on the control of the solenoids used in the EMV system and computer modeling of such control systems (Stubbs, 2000; Boie, 2001; Wang, 2001; Chang et al., 2002; Tai, 2002; Wang et al., 2002; Hoffmann and Stefanopoulou, 2003; Nitu et al., 2004; Peterson and Stefanopoulou, 2004; Kamis and Yuksel, 2005; Copeet al., 2008). However, a mass production camless engine has not yet been produced.n this study an EMV system was designed based on systems built by other engineers. The EMV engine (a semi electro-mechanical camless engine), which enables electro-mechanical operation of the intake valve, and a standard engine were tested to understand the effect of EMVs on engine performance and emissions at different engine speeds under load. During the engine tests engine valve timing, valve opening duration and ignition timing were kept constant to observe the effects of the EMV system alone. 2. Electro-mechanical valve system The components that comprised the electro- mechanic valve actuator (EMVA) were similar to those of other systems (Stubbs, 2000; Boie, 2001; Wang, 2001; Chang et al., 2002; Tai, 2002; Wang et al., 2002; Hoffmann and Stefanopoulou, 2003; Nitu et al., 2004; Peterson and Stefanopoulou, 2004; Kamis and Yuksel, 2005; Copeet al., 2008). They included an engine valve, two electro-magnets, an actuator spring and a valve spring. The diagram of an EMVA that is commonly used is given in Fig. 1. Principally, the actuator is like an oscillating mass-spring combination and is activated by an electro-magnetic force. The potential energy is transferred between two springs via the core and the valve throughout normal operation. The voltage is applied to the relevant coil during the transition. The magnetic force formed overcomes the spring, friction and gas flow forces. The upper coil closes the valve and the lower coil opens it. The EMV system works in three different positions: voltage is applied to the lower coil to open the valve. The magnetic traction force formed moves the core and opens the valve. When no voltage is applied to the coils, the core is centered exactly in the middle of two coils and in a neutral position. In this position, the valve spring and the actuator spring are compressed equally and the valve is half open. Voltage is applied to the upper coil to close the valve. The core moves upwards under the effect of the magnetic force and closes the valve. In some studies, the electrical power requirement of the EMV system is given as about 3 kW and the operating voltage that can meet this requirement would be 42 V (Trevett, 2002; Kassakian et al., 2005). An E-shaped electro-magnet is recommended as the most suitable magnet type for the EMV driving system (Nitu et al., 2004). The springs are very important to the continuous operation of the valve and they also influence the valve transition time (Wang et al., 2002; Kamis and Yuksel, 2003). The moving core completesmost of its movements with the help of the energy stored in the springs. The spring force adds to the magnetic force until the point at which half of the movement length is reached for the effective coil. After that point, it imposes a force against the magnetic force. Therefore, the selection of the springs in EMV systems is of paramount importance. 3. Electro-mechanical valve system design The appearance of the designed EMV system on the engine cylinder head is given in Fig. 2 and a block diagram of the system in Fig. 3. The EMV control system consists of a timing disc installed on the camshaft, an inductive sensor used for sensing the valve timing on the timing disk, a control unit that controls the actuator with sensor signals, a power supply that feeds the EMV control unit (18 V), an actuator that opens and closes the valve by forming magnetic force, an actuator spring and a valve spring, and a power supply with 33 V rated voltage, which feeds the EMV system (Fig. 4). The sensor that senses the valve timing on the disc which rotates with the camshaft, transmits the signal to the EMV control unit. In accordance with the signals received from the sensor, the EMV control unit directs the 33 V voltage to the lower solenoid coil. With the activation of the lower solenoid coil, the core (armature) inside the solenoid coil overcomes the valve spring force with the help of the magnetic force and opens the valve completely (Fig. 3). Thus, the EMV control unit provides opening and closing of the valve according to the timing signals received from the sensor. The EMV control system consists of two units that have the same structure: one of the units controls the lower solenoid coil, the other controls the upper solenoid coil. Upon receiving the sensor output signal, the unit that controls the solenoid coil switches the current by saturating the Darlington connected transistors and transmits the current to the lower solenoid coil via the power transistor. The same signal is used for the control of the upper solenoid coil. After the sensor output signal is inverted by a “NOT” gate, thupper solenoid coil is activated via a power transistor, as described above. 4. Experimental studies An experimental study was performed to compare the performance and emissions of a spark ignited engine (SI) containing an EMV system and an electro-mechanically controlled intake valve with an engine containing a traditional valve system (standard engine). We also aimed to test the efficiency of the EMV system. The experimental conditions included six engine speeds (1600, 2000, 2400, 2800, 3200 and 3600 r/min) under full load and other relevant parameters (Table 1). The experimental set-up (Fig. 4) consisted of a test engine, dynamometer (DC dynamometer), fuel flow meter, exhaust gas analysis system, EMV system and EMV system test apparatus. The technical specifications of the test engine used in the experiments are given in Table 1. The test engine was first tested without EMV under full load, at various engine speeds. Then the same engine was equipped with the EMV system and tested under the same conditions for comparison. To test the EMV control unit and electrical parts, a Picoscope ADC 212 general purpose PC oscilloscope (UK) was used. The measurements of the EMV system and those of the engine performance were obtained simultaneously. Emissions were measured with an MRU DELTA 1600 L exhaust gas analyzer (Germany). The specifications of the exhaust gas analyzer are given in Table 2. Data were collected for engine torque, engine power, specific fuel consumption, excess air factor (), CO, HC and Nox emissions. In addition, the variation in the current flowing through the lower and upper coils and sensor signal data were recorded. 5. Results and discussion 5.1 Engine performance Fig. 5 shows the torque changes for the EMV engine and the standard engine. Compared with the standard engine, the EMV engine achieved a 6.4% higher torque at 1600 r/min, a mean increment of 9% between 2000 and 3200 r/min engine speed, and 2.8% higher torque at 3600 r/min. The valve opening and closing speed depends on several conditions, especially the control algorithm. However, valve opening and closing profiles are more square-shaped in EMV applications. The intake valve is fully open for a longer time in the operation of an EMV engine because the intake valve opens faster. In addition, differences in the valve cross-sectional areas have a considerable influence on engine performance and emissions (Ergeneman et al., 1998). The computed cross-sectional area under the intake valve lift curve of the standard engine used in this study was 17.7% lower than that of the EMV engine (Fig. 6). An increased valve cross-sectional area in the first half of the induction stroke has significant importance for many reasons. For example, it produces a greater flow area as the piston starts to pull in a fresh charge. The opening of the intake valve occurs faster with the EMV system, enabling the engine to have an increased valve overlap area. Valve overlap is the point near the piston top dead center (TDC) in the 4-stroke cycle where both the intake and the exhaust valves are open at the same time. In this study, the computed valve overlap cross-sectional area of the EMV engine was about 310% greater than that of the standard engine (Fig. 6). The negative work necessary to suck air into the cylinder is reduced by increased valve overlap. Also, an increase in the valve overlap amount implies an increase in the intake manifold pressure (Hammar-lund, 2008; Leroy et al., 2008). The increase in the valve overlap cross-sectional area is equivalent to extending the valve overlap period in a standard engine (Ergeneman et al., 1998). At low speed, the effect of valve overlap is to re-introduce exhaust gasses into the combustion chamber. This is known as generating internal exhaust gas re-circulation (EGR) or internal EGR. Extending the valve overlap period facilitates an internal EGR. However, extending the valve overlap period at low speeds causes a decrease in engine performance (?nar, 1998; Akba, 2000). When the engine speed was near 2000 r/min in the operation of the standard engine, the excess air factor was determined as <1 (Fig. 7). The reason that the excess air factor was higher in the EMV engine than in the standard engine at the same engine speed, was that the air mass increased because of the more rapid opening of the intake valve. Because the remaining fuel mass was the same in both engines, the mixture became poorer in the EMV engine. The torque increase attained by the EMV system was reduced at low and high engine speeds because the fresh air-fuel mixture taken inside the cylinders mixes with the exhaust gases. Some of the fresh air-fuel mixture is exhausted together with waste exhaust gases in the operation of the standard engine. However, the torque increase was minimized because of the decrease in powerlost as a result of friction in the valve system. Changes in the power o