喷雾引导型直喷汽油缸内流混合气的形成和燃烧过程的分析

1、Analysis of the In-Cylinder Flow, Mixture Formation and Combustion Processes in a Spray-Guided GDI EngineSung-Jun Kim, Young-Nam Kim and Je-Hyung Lee Hyundai Motor CompanyCopyright . 2008 SAE International在喷雾引导直喷汽油缸内流混合气的形成和燃烧过程的分析ABSTRACTThe purpose of this paper is to investigate the air/fuel mixt

2、ure formation and combustion characteristics in a spray-guided GDI engine using a commercial code,STAR-CD. This engine adopted the outwardly opening injector located in the center of cylinder head, which forms a hollow cone spray. The spray injection was modeled arranging multiple points using rando

3、m function along the ring-shaped nozzle exit. To predict the breakup of spray, Reitz-Diwakars breakup model was used, and the model constants were calibrated against published experimental data in a constant volume chamber. The validated spray models were applied to the analysis of spray behavior an

4、d mixture formation process inside the engine combustion chamber under operating condition of ultra-lean mixture (4). To predict the combustion process, the modified eddy breakup combustion model was applied. The present approach reasonably predicted the spray behavior, the mixture distribution near

5、 the spark plug, and flame propagation inside the combustion chamber. The calculated combustion pressure had a good agreement with the engine test results. Furthermore, the variations of the geometries of intake port and combustion chamber, the split injection parameters, and compression ratio were

6、evaluated. The result shows that the enhanced tumble flow can deteriorate the mixture distribution of the hollow cone spray, and therefore decreases the burning rate. Also, the influence of injection timing and compression ratio on the quality of the stratified mixture at the spark was well predicte

7、d.摘要本文的目的是研究空气/燃料混合气的形成和在喷雾引导GDI发动机使用的是商业代码，STAR-CD的燃烧特性。这台发动机采用向外开放的喷油器位于缸盖的中心，形成一个空心锥形喷雾。为蓝本安排使用随机函数沿环形喷嘴出口的多点喷射注射。赖茨，Diwakar预测喷雾解体，解体模型，模型校准常数，对在一个恒定体积室发表的实验数据。喷雾模型验证，适用于喷射发动机燃烧室超稀混合（4）根据经营条件的行为和内部混合气形成过程的分析。预测燃烧过程，改良涡破裂燃烧模型的应用。目前的做法合理预测喷雾行为，火花塞附近的混合分布，燃烧室内部和火焰传播。计算燃烧压力与发动机试验结果吻合良好。此外，进气口和燃烧室，分流进

8、样参数，压缩比的几何形状的变化进行了评价。结果表明，增强滚筒流恶化的空心锥形喷雾混合分布，并因此降低了燃烧率。此外，喷油定时和分层的混合物在火花塞的质量压缩比的影响，以及预测。INTRODUCTIONRecently emission regulations of CO2 which mainly causes global warming become more stringent. Also, higher thermal efficiency is desperately demanded as crude oil price goes up. Gasoline direct-injec

9、tion engines have a promising potential for fuel consumption reduction for gasoline engines because of lower fuel consumption rate and higher performance compared to conventional gasoline engines. The fuel consumption of a spray-guided GDI engine is much less than that of conventional PFI engine due

10、 to fuel stratification under overall ultra-lean mixture and unthrottled operation 1. 引言最近的二氧化碳的排放法规，主要是导致全球变暖更加严格。此外，热效率高，迫切要求原油价格上涨。汽油直喷式发动机有前途的潜力，因为较低的燃油消耗率和更高的性能，与传统的汽油发动机相比汽油发动机的燃料消耗减少。喷雾引导GDI发动机的油耗比传统PFI的发动机由于燃油分层下的整体超稀混合的节流运作1少得多。In the engine, injector is located near spark plug and its holl

11、ow cone spray directly reaches very close to spark plug. Rich mixture is formed at spark plug, and the flame propagates from rich region to surrounding lean mixture. The latest spray-guided GDI engine adopts higher pressure injection system to enhance the quality of atomization of fuel spray. It add

12、itionally adopts a piezo actuated injector which features quick response and split injection with short interval. Therefore, the injection system can be advantageous for the formation of stratified mixture and reliable ultra-lean combustion at part load 2, 3.在发动机，喷油器位于靠近火花塞和空心锥形喷雾直接到达非常接近火花塞。丰富的混合物，

13、在火花塞形成，从丰富的地区周围的稀混合火焰传播。最新的喷雾引导GDI发动机采用更高的压力喷射系统，以提高燃油喷雾的雾化质量。另外它采用了压电驱动的喷油器，它具有快速反应和短的时间间隔分割注射。因此，喷射系统，可以有利于形成分层混合和可靠的超稀薄燃烧，在部分负荷2，3。 In a spray-guided GDI engine, to extend the stratified operation range and acquire the combustion stability, the optimization of the mixture formation is very import

14、ant. Generally the mixture formation of a GDI engine depends on various engine parameters and operating conditions. To optimize these parameters by only experimental method is time-consuming job, and its difficult to investigate the complicated phenomenon of mixture formation and its combustion. 在喷雾

15、引导GDI发动机，延长分层经营的范围和取得的燃烧稳定性，优化混合气的形成是非常重要的。一般来说，一个GDI发动机的混合气的形成依赖于各种发动机参数和运行条件。为了优化这些参数，通过实验的方法是费时的工作，和复杂的混合气形成及其燃烧现象很难调查。To overcome these restrictions, 3D in-cylinder flow simulation is essential. This can give researchers a better understanding of the flow, mixture formation and combustion proces

16、s in a combustion chamber in detail, and a guide to the design of GDI combustion system. Actually, Toyota, Siemens and Delphi et al. have applied CFD tools to the development of a GDI injection and combustion system 1, 4, 5, 6. 为了克服这些限制，缸内三维流模拟是必不可少的。这可以让研究人员更好地理解流，混合气的形成和燃烧室燃烧过程中的细节，以及GDI的燃烧系统设计指南。

17、其实，丰田，西门子，德尔福等。应用CFD工具发展的一个GDI喷射和燃烧系统1，4，5，6。In this study, firstly fundamental investigation into fuel spray characteristics and air motion driven by fuel spray were analyzed in a constant volume chamber. Secondly the stratified mixture formation and its combustion characteristics in a spray guided

18、 GDI engine was analyzed at part load with ultra-lean mixture. Under this operating condition, variations of tumble flow, split injection parameters and compression ratio were considered. The analysis results were presented and compared with experiments.在这项研究中，首先基本成燃料喷雾特性和燃油喷射推动空气运动的调查分析，在一个恒定体积室。其次

19、分层混合气的形成和喷雾引导GDI发动机的燃烧特性进行了分析，超稀混合在部分负荷。在此操作条件下，滚筒流量的变化，分裂注入参数和压缩比被认为是分析结果与实验进行了介绍和比较.MODEL FORMULATIONThis analysis was carried out using a commercial code of STAR-CD 9. It can solve the full three-dimensional compressible averaged Navier-Stokes equations. Turbulent flow inside the combustion chamb

20、er was modeled using the standard K-. model模型公式此进行了分析，使用商用密码的STAR-CD9。它可以解决的全三维可压缩平均Navier-Stokes方程。内的燃烧室湍流模型，使用标准的K-模型.Spray modeling for the calculation is the following:The spray-guided engine is equipped with the outwardly opening injector which forms a hollow cone spray in its ring-shaped nozzl

21、e exit as shown in Figure 1. The brief specifications of the injector are listed in Table 1. The nozzle exit with a constant radius is modeled as multiple points arranged along a circle with same radius. The locations of injection points as well as injection direction are determined by random functi

22、on via user-subroutine.The initial drop size at nozzle exit was assumed to be the injector needle stroke, approximately 30 m at a fuel pressure of 200 bar 2. The width of injected spray was considered negligible due to very thin liquid sheet喷雾模拟计算如下：发动机配备的喷雾引导向外开放的喷油器在其环形喷嘴出口形成一个空心锥形喷雾，如在图1所示。喷油器的简要

23、规格列于表1。恒定半径的喷嘴出口为蓝本沿半径相同的圆排列的多个点。注射点的位置以及喷射方向，决心通过用户子程序的随机函数。初始液滴尺寸在喷嘴出口被认为是喷油器针阀行程，大约30微米，在200巴的燃油压力2。注入喷雾宽度被认为是微不足道的，由于非常薄的液体表面After fuel spray exits the nozzle, the Lagrangian parcel tracking method was used to predict the spray behavior. To predict the breakup of spray, Reitz-Diwakars breakup mo

24、del was used 8. The interaction of turbulence and spray was considered but no collision and coalescence between droplets was considered because of the uncertainty problem with these models.The evaporation of spray and heat transfer between gas phase and spray was predicted by the standard model in S

25、TAR-CD.喷嘴燃油喷射退出后，拉格朗日包裹跟踪方法用来预测喷雾行为。预测喷雾解体，赖茨Diwakar的解体模型8。动荡和喷雾的相互作用被认为是，但没有碰撞和液滴之间的聚结，因为这些模型的不确定性问题的考虑。STAR-CD的标准模型预测之间的气相和喷雾的喷雾和传热蒸发。.For fuel, isooctane was used as a surrogate fuel of gasoline. Its liquid properties were from KIVA fuel library and linked to STAR-CD via a subroutine 7.用于燃料，异辛烷，作

26、为汽油的替代燃料的使用。其液体性质的KIVA燃料库和链接通过STAR-CD的子程序7。In this study, turbulent combustion was simply modeled with modified eddy breakup model to alleviate the overestimation of reaction rate near wall. To ignite the mixture, ignition temperature during ignition was set to 2000K.在这项研究中，湍流燃烧模型改进的涡破裂模型，以减轻反应率近壁高估

27、。在点火点燃的混合物，点火温度为2000K。The main specifications of the engine are listed in Table 2 10. The intake ports have siamese type arms that mainly generates tumble. The injector located at the center of the cylinder head is close to the ignition plug as shown in Figure 2. To precisely investigate the interac

28、tion between spray and flow near spark plug, the complicated configurations of the injector nozzle tip and spark plug were modeled. Since the geometry of the ports and combustion chamber are symmetrical, only half the engine was modeled to save the computation time. Computational mesh was generated

29、via es-ice 11.发动机的主要规格列于表210。进气口有连体式武器，主要作用烘干。在位于缸盖中心的喷油器是靠近火花塞，如图2所示。喷油器喷嘴和火花塞附近的喷雾和流之间的相互作用，以精确的调查，复杂的配置为蓝本。由于港口和燃烧室的几何形状是对称的，只有一半的发动机为蓝本，以节省计算时间。通过ES-ICE11，计算网格生成。Table 1. Injector specifications 10ActuationPiezoTypeOutward-openingNominal spray cone angle90Static flow rateMore than 35 g/sFuel pre

30、ssure range50-200 bar表1。喷油器规格10驱动压电键入向外开放标称喷雾锥角90静态流量超过 35 g/s燃油压力范围50-200 barFigure 1. Schematic of the spray-guided GDI injector and applied injection model图1。喷雾引导GDI的喷油器示意图和应用注入模型Table 2. Engine specificationsBore x Stroke88 x 97Compression ratio10.5, 12.0Displacement2.4 L (4 Cyl.)InjectorPiezo-a

31、ctuated outwardly-opening typePistonFlat & shallow bowl表2。发动机规格缸径x冲程88 x 97压缩比10.5, 12.0排气量2.4 L (4 Cyl.)喷油驱动向外开放型活塞平浅碗状Figure 2. The geometry and mesh of the engine图2。发动机的几何形状和网格The boundary conditions for both intake and exhaust ports were treated as pressure boundary with a constant total pressur

32、e. The calculation started just before intake valve opening.被视为一个恒定的总压力与压力边界的边界条件为进气口和排气口。计算开始之前进气阀门的开度。RESULTSCalibration of spray model in a constant volume chamberFor the calibration of spray modeling, its related model constants were adjusted against the spray images in a constant volume chamber

33、. The static flow rate is 35 g/s at injection pressure of 200 bar 2. The injection velocity at nozzle exit was assumed to be about 200 m/s.结果在一个恒定体积室喷雾模型的校准对于校准喷雾建模，其相关的模型常数进行了调整，对在定容腔的喷雾图像。静态流量为35克/ s的注射压力200巴2。在注射喷嘴出口速度假设为200米/秒左右。(c) Velocity fields on the section through the injector center（c）通过

34、喷油器中心部分的速度场Figure 3. Comparison between spray visualization and calculation result in a constant volume chamber图3。在一个恒定体积室喷雾可视化和计算结果之间的比较Figure 3 shows the comparison between experiment and the computed spray shape. The computed hollow cone spray and its penetration as shown in Figure 3(b) are appar

35、ently agreed with the spray image. The spray induced velocity field was also shown in Figure 3(c). The recirculation zone was formed at the lower end of spray and fuel droplets rotate within vortex. Entrainment flow into spray at the upstream of spray and center flow in direction to the injector tip

36、 inside the hollow cone spray were formed. From the results, our method well predicts the spray characteristic of spray-guided injector and the spray induced airflow.图3显示了实验和计算的喷雾形状之间的比较。计算空心锥形喷雾，其普及率在图3（b）所示，显然是同意与喷图像。喷雾诱导速度场也显示在图3（c）。在下端内旋涡旋转喷雾和燃料液滴形成回流区。喷雾和中心内的空心锥形喷雾注射器尖方向流动的上游夹带进入喷流的形成。从结果来看，我们的

37、方法以及预测的喷雾引导喷油器和喷雾诱导气流的喷雾特性。The analysis of Spray-Guided GDI EngineAfter the validation of spray models, these models were applied to the calculation of real engine operating condition.As mentioned earlier, the operating point for the calculation is a stratified and ultra-lean condition, whose detail

38、s are listed in Table 3.喷雾引导直喷汽油分析喷雾模型的验证后，这些模型被应用到实际发动机运行条件下的计算。如前所述，计算的经营点，是一个分层和超精细的条件下，其在表3中所列的细节。Table 3. Engine operating conditions and assumed wall temperatures for the baseline caseEngine speed(rpm)2000BMEP(bar)2.0Intake manifoldpressure(bar) / temperature(K)1.0(unthrottled)/ 300Air excess

39、ratio()4Intake valve timing(CA, BTDC/ABDC)-11 / 67Injection pressure(bar)200Cylinder head(K)390Cylinder liner(K)390Piston(K)410表3。发动机的工作条件和假设为基准的情况下壁面温度发动机转速(rpm)2000BMEP(bar)2.0进气歧管压力(bar) / 温度(K)1.0(unthrottled)/ 300空气压缩率()4进气门(CA, BTDC/ABDC)-11 / 67注射压力(bar)200缸盖(K)390缸套(K)390活塞(K)410The fuel was

40、 injected in two steps close to TDC as shown in Figure 4. The injection profile used in this study was simplified to be a simple square wave function considering a relatively prompt and stable response especially for the piezo-actuated injector 2. The spark timing is located between two injections.燃

41、料注入两个步骤，贸发局在图4所示。在这项研究中所使用的注入剖面被简化为一个简单的方波函数，考虑相对迅速和稳定的响应，特别是压电驱动式喷油器2。点火正位于两针之间。Figure 4. Injection rate and ignition timing for the baseline case图4。注射率和点火时间为基准的情况下After the start of the first injection, the hollow cone spray was found in Figure 5. The recirculation zone was formed at the lower end

42、 of spray as shown in Figure 6. A part of spray was located near the spark plug by the recirculation flow at -27ATDC near the ignition timing. The flow oriented to the injector tip inside the hollow cone spray was formed due to pressure drop near nozzle exit.空心锥形喷雾开始第一次注射后，被发现在图5。回流区形成于低端的喷图6所示。靠近火花

43、塞-27止点附近的点火时间，在再循环流量，喷雾的一部分。由于喷嘴出口附近压力下降，流量为导向，以喷油器内部的空心锥形喷雾尖形成。Figure 5. Hollow cone spray in the combustion chamber图5。燃烧室内空心锥形喷雾Figure 6. Velocity fields on the section through the injector and the spark plug图6。部分通过喷油器和火花塞上的速度场Figure 7 shows the computed distribution inside the combustion chamber.

44、 The first injected spray evaporated mainly at the lower part of spray, and a toroidal-shaped fuel cloud was formed at -30ATDC. At the spark timing of about -27 ATDC, stratified richmixture was located at the spark plug. The second injected spray also reached near the spark plug at -21 ATDC. Evapora

45、ting fuel cloud of the second spray was merged into the previously formed toroidal-shaped fuel cloud. The fuel concentration in the cloud decreased steadily by diffusion and combustion. Although a little of fuel vapor from the early injected spray distributed on piston surface, any spray didnt direc

46、tly hit the piston.图7显示了燃烧室内部的计算分布。首先注入喷雾蒸发主要在下部喷雾，并在-30止点形成一个环形燃料云。在约-27止点，分层丰富的点火时间位于火花塞的混合物。也达到了第二次注射喷在-21止点附近的火花塞。第二喷雾蒸发的燃料云并入以前形成的环形型燃料云。在云中的燃料浓度逐渐下降的扩散和燃烧。虽然从早期注入活塞表面上分布的喷雾燃料蒸气的一点，任何喷雾没有直接命中活塞。Figure 7 distribution on different sections through the combustion chamber at various crank angles (b

47、aseline)图7分布在不同的部分，通过在不同曲柄角度燃烧室（基线）Figure 8 shows the distribution of temperature inside the combustion chamber during combustion. After the ignition, the flame kernel was developed at -24ATDC during the second injection. At -15 ATDC, the flame started to spread around the periphery of toroidal shap

48、ed fuel cloud, which was described as dashed circle. The temperature of inner rich region was relatively lower.图8显示了燃烧室内部燃烧过程中的温度分布。点火后，火焰内核发展在-24止点在第二次注射。在-15止点，火焰开始向四周扩散的环形燃料云，它被描述为虚线圆圈的边缘。丰富的地区内的温度相对较低。Figure 8. Temperature distribution on the section through the injector and the spark plug (base

49、line)图8。温度分布对部分通过喷油器和火花塞（基线）The application of VCM (Variable Charge Motion) VCM is generally used to intensify the tumble flow and turbulence intensity. In this study the effect of increased tumble flow on mixture formation and its combustion in a spray-guided engine was investigated. VCM was instal

50、led in the intake manifold and the configuration of VCM is shown in Figure 9. While VCM is operating like the figure, air flow velocity increases with passing through reduced flow area. The air with highly increased velocity flows along the upper region of the intake port and results in strong count

51、erclockwise tumble inside the combustion chamber as shown in Figure 10(b).应用的VCM（可变电荷运动） VCM是通常用来加强滚筒流和湍流强度。在这项研究中，增加其在喷雾制导发动机的燃烧混合气的形成和滚筒流的影响进行了调查。氯乙烯被安装在进气歧管和氯乙烯单体的配置，如图9所示。 VCM是像图，气流穿过流面积减少的速度增加。与高增长速度的空气流动沿上游地区的进气口和强烈逆时针滚筒内的燃烧室，在图10（b）所示的结果。Figure 9. Configuration of VCM图9。氯乙烯单体的配置Figure 11 show

52、s the variation of tumble ratio and turbulence according to the application of VCM. As expected, both the tumble ratio and turbulence increased highly in comparison with the case of w/o VCM. Although there is a little decrease in the tumble ratio due to the interaction with injected spray, higher tu

53、mble of the case of w/ VCM sustained during combustion.图11显示了滚筒比例的变化和动荡根据氯乙烯单体的应用。正如所料，滚筒比例和动荡增加在比较高的W / O氯乙烯。虽然是在滚筒比例略有下降，由于注入喷雾，更高的W / VCM的情况下持续燃烧过程中的烘干的相互作用。Figure 10. Variation of velocity distribution on the section through the injector and the spark plug close to TDC by the application of VCM

54、(w/o spray)图10。节上通过喷油器和火花塞附近的VCM应用贸发局（W / O型喷雾速度分布的变化）Figure 11. Variation of tumble ratio and turbulence by the application of VCM图11。滚转比和湍流变化的VCM应用Figure 12. Spray and velocity distribution on the section through the injector and the spark plug at the end of the 1st injection for the case of w/ VC

55、M图12。在第一次注射的结束部分为W / VCM的情况下通过喷油器和火花塞的喷雾和速度分布Figure 12 shows spray and velocity distribution after the end of the first injection for the case of w/ VCM. More injected fuel exists at the spark plug in comparison to the case of w/o VCM as shown in Figure 5 because the tumble velocity from the intake

56、side in direction to the spark plug is higher. High velocity was found under the spark plug as shown in Figure 12(b) because the direction of the injected spray was a little changed close to the spark plug due to the interaction with strong tumble flow.图12所示为W / VCM的情况下，第一次注射结束后，喷雾和速度分布。更多的喷油存在，在比较的

57、情况下，如在图5所示的W / O氯乙烯的火花塞，因为火花塞在方向上的进气侧的滚筒速度较高。高流速下火花塞，发现如图12所示（b）由于注入喷雾方向靠近火花塞由于具有较强的滚筒流的相互作用改变了一点点。Figure 13 shows that increased tumble largely affect the mixture formation and deteriorates the distribution quality of mixture inside the combustion chamber. At -27 ATDC, more fuel droplets near the s

58、park plug caused richer mixture at the spark plug than the case of w/o VCM as shown in Figure 7. At -10 ATDC, unlike the case of w/o VCM, a toroidal-shaped fuel cloud was deformed and highly rich zone was formed in the neighborhood of the spark plug because the increased counterclockwise tumble results in overlap of fuel clouds of intake and exhaust side. Figure 14 shows that the =1 isosurface of the case of w/ VCM was also s