기체구 분사 모델을 이용한 CNG 직접분사식 인젝터 분사 수치해석 기법

최민기 ( Mingi Choi ),박성욱 ( Sungwook Park ) 한국분무공학회 2016 한국액체미립화학회지 Vol.21 No.1

This paper describes the modeling of CNG direct injection using gaseous sphere injection model. Simulation of CNG direct injection does not need break up and evaporation model compared to that of liquid fuel injection. And very fine mesh is needed near the injector nozzle to resolve the inflow boundary. Therefore it takes long computation time for gaseous fuel injection simulation. However, simulation of CNG direct injection could be performed with the coarse mesh using gaseous sphere injection model. This model was integrated in KIVA-3V code and RNG k-ε turbulence model needs to be modified because this model tends to over-predict gas jet diffusion. Furthermore, we preformed experiments of gaseous fuel injection using PLIF (planar laser induced fluorescence)method. Gaseous fuel injection model was validated against experiment data. The simulation results agreed well with the experiment results. Therefore gaseous sphere injection model has the reliability about gaseous fuel direct injection. And this model was predicted well a general tendency of gaseous fuel injection.

분무응용 기술 : Gaseous sphere 분사모델을 이용한 CNG 직분사 엔진 모델링

최민기 ( Mingi Choi ),송진근 ( Jingeun Song ),박성욱 ( Sungwook Park ) 한국액체미립화학회 2015 한국액체미립화학회 학술강연회 논문집 Vol.2015 No.-

This paper describes the modeling of CNG (compressed natural gas) direct injection engine using gaseous sphere injection model. Numerical modeling was conducted using KIVA-3V Release 2 code with some modifications. Three dimensional mesh included 4 valves was used for computational grid. Gaseous sphere injection model could be integrated in KIVA-3V Release 2 code with some modification of liquid injection model and RNG (re-normalization group) k-ε turbulence model. This model could simulate gaseous sphere injection using coarse mesh which saves calculation time. The fine mesh is not required to resolve the inflow boundary for gaseous sphere injection. Likewise with liquid injection model, gaseous spheres are injected as parcels which represent a group of gaseous spheres and these parcels evaporate at a time. The evaporation of gaseous spheres occurs without energy change. Particularly, poppet type injector was used for CNG direct injection therefore hollow cone type injection model was modified. The RNG k-ε turbulence model need some modifications. Since this model is known to over-predict gas jet diffusion, turbulence kinetic energy and turbulence length scale values were adjusted depend on grid location. The modified RNG k-ε turbulence model is applied only for the injection period. After the fuel injection was finished, the conventional RNG k-ε turbulence model is applied. Chemkin chemistry solver 2 was coupled with KIVA-3V Release 2 code to simulate combustion process of CNG fuel. CNG is represented by methane and GRI 3.0 mechanism which optimized for combustion process of natural gas was used. In order to calculate the turbulent flame speed, G-equation model was used in which flame front is specified by zero level set of G. In addition, experiments of gaseous fuel injection was performed for gas-jet visualizations using PLIF (planar laser induced fluorescence) method. For safety reasons, compressed nitrogen was used instead of compressed natural gas in the experiments. The tracer which plays an important role in PLIF experiments was acetone that has a very low boiling point, a high saturation pressure, a good fluorescence and low toxicity. Furthermore, experiments of CNG combustion was performed using single cylinder SI (spark ignition) engine. For CNG direct injection, poppet type gaseous fuel injector was used and this injector was centrally mounted. In this study, the simulation results of CNG direct injection engine were compared to experimental results. The gaseous sphere injection model can reliably predict CNG direct injection. Furthermore, the results of ignition and combustion process agreed well with experiment results.

Numerical and experimental study on effects of fuel injection timings on combustion and emission characteristics of a direct-injection spark-ignition gasoline engine with a 50 MPa fuel injection system

Kim, Taehoon,Song, Jingeun,Park, Junkyu,Park, Sungwook Elsevier 2018 Applied thermal engineering Vol.144 No.-

<P><B>Abstract</B></P> <P>In this study, an increase in injection pressure was proposed as a solution to the problem of exhaust emissions, such as soot, NOx, CO, HC, in direct-injection spark-ignition gasoline engines. Mixture formation and combustion process were analyzed with KIVA-3V release 2 code. Combustion pressure and emission data were also measured experimentally. To validate the models used in simulation, spray tip penetration for various injection pressures, and combustion pressure for various injection timing and injection pressure combinations were compared with experimental data. The simulation using a constant-tuned models showed reliable results and simulations were carried out using validated models. When the fuel is injected while the intake flow is developing, the mixture homogeneity was reduced and combustion speed decreased. When the fuel is injected after the intake flow has fully developed and injection pressure was high, the combustion speed increased. High injection pressure was effective in increasing the mixture homogeneity in case of late injection timing. Therefore, increasing thermal efficiency without deteriorating exhaust emissions is possible when an injection pressure up to 50 MPa is used with late injection timing.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High pressure injection up to 50 MPa was adopted for direct-injection spark-ignition gasoline engine. </LI> <LI> Numerical analysis was carried out to analyze the experimental results. </LI> <LI> High injection pressure is effective to reduce fuel film formation. </LI> <LI> Late injection can be used to increase turbulence intensity using 50 MPa injection pressure. </LI> </UL> </P>

THE EFFECT OF SPRAY ON COMBUSTION AND EMISSION IN DIRECT-INJECTION SPARK-IGNITION ENGINES

( Kyoungdoug Min ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-

In the light of energy and environmental concerns, the CO₂ regulation for light-duty vehicles has become stricter than ever. Direct-injection spark-ignition (DISI) engine with a turbocharger is regarded as a major technology to improve the thermal efficiency and to lower the specific fuel consumption. However, the direct injection of gasoline leads the inhomogeneous air-fuel mixture in the cylinder and the fuel film deposition on the walls. As a result, the particulate matter (PM) emission is deteriorated compared to conventional port fuel injection engines. European Union enforced the emission regulation on the particulate number (PN) of DISI engine powered vehicles as 6×10¹¹/km from September 2017. To satisfy the stringent regulation without an after-treatment system, an in-depth understanding of the spray and combustion fundamentals, as well as a substantial optimization effort for the engine operating strategy, are required. The PM emission arises from the local fuel-rich mixture around the fuel film in DISI engines so that the spray injection plays the key role in the PM reduction. In this presentation, both experimental and numerical investigation on the effect of spray injection in a DISI engine will be covered. First, the potential of injection strategy on the PN emission level will be discussed based on the PM measurement in both metal and optical-accessible single-cylinder research engine. Then, the combustion and soot emission modeling and their application to CFD simulation will be presented to propose an efficient and reliable tool for the optimization of engine system. The rig-experiment enables the fundamental understanding of spray behavior and provides the valuable reference data for the model validation. This talk also discusses the spray evolution including penetration length, spray cone angle, and sauter mean diameter under various injection conditions. Finally, the measurement and modeling work on the spray-wall impingement and fuel film formation will be presented.

직접분사식 단기통 디젤엔진에서 다단분사에 따른 연소 및 배기특성

허정윤(Jeong Yun Heo),차준표(Junepyo Cha),윤승현(Seung Hyun Yoon),이창식(Chang Sik Lee) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5

The purpose of this work is an experimental investigation combustion and emission characteristics in DI diesel engine applied multiple injection strategy. In order to analyze the effect of multiple injection, single-cylinder DI diesel engine was operated under electrically controlled fuel injection system. In this study, multiple injections were injected as two types of multiple injection that were defined as the pilot injection and the post injection. The pilot injection and the post injection was injected 30% of total fuel injections mass quantity. The results of multiple injection were compared to those of single injection and each multiple injection types. To investigate for a low speed engine and middle range load, the experimental conditions were conducted under a fixed engine speed and constant stoichiometric ratio condition. The combustion results show that each multiple injections decreases peak heat release rates but increases indicated mean effective pressure. The emissions results that pilot injection increases emissions but post injection reduces NO<SUB>x</SUB>, HC and CO emissions.

Study of regulated emissions and nanoparticle characteristics of light-duty direct-injection vehicles fuelled with gasoline and liquefied petroleum gas in the New European Driving Cycle and the Federal Test Procedure 75 driving cycle

Jang, Wonwook,Ko, Ahyun,Baek, Sungha,Jin, Dongyoung,Choi, Kwanhee,Myung, Cha-Lee,Park, Simsoo Professional Engineering Publishing Ltd 2015 Proceedings of the Institution of Mechanical Engin Vol. No.

<P>This study evaluated the pollutants and nanoparticles, the fuel economy and the levels of carbon dioxide emissions of vehicles equipped with a 1.6 l direct-injection spark ignition engine fuelled by gasoline or by liquefied petroleum gas. The nanoparticles were analysed using a particle measurement system that is used in Europe for regulatory purposes. A fast-response particle size and number spectrometer (model DMS500) were used to characterize the size-resolved particle distributions. The vehicle was tested on a chassis dynamometer for the New European Driving Cycle and Federal Test Procedure 75 in its factory default state (gasoline version) and modified state (for liquefied petroleum gas fuel), and the results were compared. The liquefied-petroleum-gas direct-injection vehicle emitted significantly lower levels of total hydrocarbons than did the gasoline direct-injection vehicle. However, the levels of nitrogen oxide emissions from the liquefied-petroleum-gas direct-injection vehicle were equivalent to those from the gasoline direct-injection vehicle. Because of the higher combustion and exhaust temperatures and relatively higher loads imposed during the driving cycles, the liquefied-petroleum-gas direct-injection vehicle showed a slightly higher level of nitrogen oxide emissions. The particle emissions from the vehicles were mainly affected by the vehicle driving conditions of the test driving cycles. In particular, the particle emissions from the vehicle were pronounced in the cold-start and accelerating phases of the emission certification standards. The nanoparticles from the liquefied-petroleum-gas direct-injection vehicle were significantly fewer in number, exhibiting a reduction of over 99%.</P>

Effects of different piezo-acting mechanism on two-stage fuel injection and CI combustion in a CRDi engine

Jin-Su Kim,Juwan Kim,Seokcheol Jeong,Sangilk Han,이진욱 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.12

In this study, the effects of two piezo injectors operated by different mechanisms on multi-injection and Compression ignition (CI) combustion were investigated. High-pressure injectors for CI engines are divided into two categories according to the actuator: Solenoid and piezo injectors. It is commonly known that both injectors have a hydraulic circuit for fuel injection; thus, the performance of the injector is highly dependent on not only hydraulic characteristics such as volume of internal chambers and nozzle geometry, but also the actuation mechanism. Specially, the direct needle-Driven piezo injector (DPI) is introduced in this study and compared with the indirectacting Piezo injector (PI) to investigate the injection characteristics and influences on CI combustion performance by using spray visualization, injection rate measurement, and single cylinder diesel engine experiments, as well as numerical simulation for injection rate modeling of DPI. In the spray visualization experiment, a high-speed camera was used to examine spray tip penetration length and spray speed with respect to each injector. Also, in order to investigate injection rate information, which is a significantly dominant factor in combustion characteristics, the Bosch-tube method was adapted under the condition of a back pressure of 4.5 MPa, corresponding to engine motoring pressure. Also, a single-cylinder CRDi (Common-rail direct-injection) engine experiment was carried out to determine the effects of different piezo-acting mechanisms on two-stage fuel injection and CI combustion. From the key results obtained by this study, the direct needle-driven piezo injector has a faster SOI (Start of injection) and EOI (End of injection). In addition, the overall shape of the injection rate of DPI was narrow and the injection had a higher spray speed than that of PI. Also, DPI has a higher heat release rate and peak pressure, as verified by the engine experiment. In particular, it was found that DPI showed the possibility of combustion improvement when applying a pilot injection strategy.

1D 시뮬레이션 기반 GDI 인젝터의 비선형적 분사 특성 해석에 대한 연구

이진우,문석수,허동한,강진석 한국분무공학회 2023 한국액체미립화학회지 Vol.28 No.4

Multi-injection scheme is being applied to GDI combustion to reduce PM and PN emission to meet the EU7 regulation. However, very short injection duration encounters the ballistic injection region, which injection quantity does not increase linearly with injection duration when applying multi-injection. In this study, numerical studies were conducted to reveal the cause of ballistic injection and the effect of design parameters on ballistic region using 1-D simulation, AMESim. Injection rate and injection quantity were compared with experiment to validate the established model, which showed the accuracy with 10% error. The model revealed that the tendency of ballistic region coincides with the needle motion behavior, which means that parameters at the upper part of needle such as electro-magnetic force, needle spring force and needle friction force have dominant effect on ballistic injection. To figure out the effect of electro-magnetic and needle friction force on ballistic, those parameters were varied to plus and minus 10% with model. The result showed that those parameters clearly changed the ballistic region characteristics, however, the impact became insignificant for outside of ballistic region, which means that the ballistic injection is mainly influenced by initial motion of injector needle.

Fuel Spray Characteristics and Performance Analysis of a Swirl Direct Common Rail Injector (SDCRi)

Kwak Sang-Shin,Iqbal Mahmud,Choi Gil Soon,Haeng Muk Cho 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11

Common rail injection system is playing an important role in internal combustion engine technology. The technology is technically acceptable, environmentally-friendly and economically viable. This system is efficient due to variant of direct fuel injection system. Common rail fuel injection systems for internal combustion diesel engines are designed to perform the task to secure acceptable fuel spray characteristics during the combustion process at all load conditions. It’s improved driving performance and higher fuel economy results the efficient injection technology as well as it satisfy the clean environment requirement by reducing the emissions and operating engine noise. Recent advancements and advantages of common rail injection technology are undeniable superior to previous injection technologies. Under these circumstances, the swirl direct common rail injector for internal combustion diesel engine developed. In this regard, the design of the injector nozzle, helical gear type swirl spray unit and injector cap has taken into consideration. Application of these attachments follows to deliver the outstanding idle quality, unparalleled flow consistency and unrivaled durability essential for high performance electronic fuel injection. The outcome of the swirl direct common rail injection is the swirl spray characteristics that results excellent mixing with the intake air followed by uniform combustion which is finally leads to lower exhaust emission and improvement in engine efficiency. The common rail injection system features high pressure fuel rail feeding individual solenoid valves as opposed to low-pressure fuel pump feeding unit injectors, or high-pressure fuel line to mechanical valves controlled by cams on the camshaft. Therefore, at high pressure the swirl direct common rail injection system results maximum volume of fuel consumption, which is important for burning inside the engine. Moreover, the injection count is take suitable timing which ensures maximum possible spray of injection at a minimum time with respective to required rpm and motor power.

Numerical investigation of the combustion characteristics and wall impingement with dependence on split-injection strategies from a gasoline direct-injection spark ignition engine

Seo, Juhyeong,Lee, Jae Seong,Choi, Kwan Hee,Kim, Ho Young,Yoon, Sam S. SAGE Publications 2013 Proceedings of the Institution of Mechanical Engin Vol.227 No.11

<P>Highly pressurized direct injection applied to automotive vehicles was developed for better power and fuel efficiency, but it causes fuel impingement, which generates more soot emissions. In the present study, analyses of the combustion characteristics and fuel impingement were conducted with a direct-injection spark ignition engine using split-injection strategies. Full three-dimensional unsteady Eulerian–Lagrangian two-phase numerical simulations were carried out to predict the flow field and the combustion characteristics as functions of the injection duration ratio and the weight of the second pulse injection. Experimental data were coupled for verification, providing the boundary and initial conditions for the benchmark case. The results showed that the weight of injection became maximally 35% less as the weight of the second pulse injection decreased. The amount of liquid fuel film, which was influenced by the injection duration ratio, had a varying range from approximately 1% to 4%. When a greater amount of the liquid fuel film impinged on the piston surface, this induced more soot formation. However, the fuel–air mixture was the most prominent factor for determining the overall combustion characteristics. A split injection can increase the thermal efficiency and the fuel consumption rate; however, without optimization, poor combustion characteristics such as knocking, incomplete combustion and soot emissions can result.</P>