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Technical Paper

Optical Experiments on Strong Knocking Combustion in Rapid Compression Machines with Different Fuels

2019-04-02
2019-01-1142
Nowadays the strong knocking combustion involving destructive pressure wave or shock wave has become the main bottleneck for highly boosted engines when pursuing high thermal efficiency. However, its fundamental mechanism is still not fully understood. In this study, synchronization measurements through simultaneous pressure acquisition and high-speed direct photography were performed to comparatively investigate the strong knocking combustion of iso-octane and propane in a rapid compression machine with flat piston design. The pressure characteristics and visualized images of autoignition and reaction wave propagation were compared, and the correlations between thermodynamic trajectories and mixture reactivity progress were analyzed. The results show that iso-octane behaves a greater propensity to strong knocking combustion than propane at similar target pressures.
Technical Paper

Numerical Study on a High Efficiency Gasoline Reformed Molecule HCCI Combustion Using Exergy Analysis

2017-03-28
2017-01-0735
In this study, the characteristics and the advantages on engine performance of the reformed molecule HCCI (RM-HCCI) combustion fueled with gasoline were investigated by exergy analysis. The processes of fuel reforming and the closed portion of the engine cycle were simulated integrated with chemical kinetics mechanism at varied compression ratio (CR) and constant speed conditions. Results showed the fuel reforming under high temperature and oxygen-free condition by the exhaust heat recovery and electric heating assistance could drive gasoline to transform to the small-molecule gas fuels, meanwhile enhanced the chemical exergy of the fuel. The reformed fuel contributed to extending ignition delay, so less dilution required in RM-HCCI engine when expanding high load compared with gasoline HCCI engine. Thus, RM-HCCI engine could achieve higher load than gasoline HCCI engine, with the improvements by 12%, 26%, and 31% at CR17, CR19, and CR21, respectively.
Technical Paper

Numerical Investigation on Effects of Combustion Chamber Structure and Oxygen Enriched Air on Combustion and Emission Characteristics of Marine Diesel Engine

2018-09-10
2018-01-1786
In order to improve the combustion and emissions for high-speed marine diesel engines, numerical investigations on effects of different combustion chamber structures combined with oxygen enriched air have to be conducted. The study uses AVL Fire code to establish three-dimensional combustion model and simulate the in-cylinder flow, air-fuel mixing and combustion process with the flow dynamics metrics such as swirl number and uniformity index, analyze the interactional effects of combustion chamber structures and oxygen enriched air against the experimental data for a part load operation at 1350 r/min, find the optimized way to improve engine performance as well as decrease the NOx and soot emissions. The novelty is that this study is to combine different oxygen concentration with different combustion chamber structures including the re-entrant chamber, the straight chamber and the open chamber.
Technical Paper

Numerical Investigation on Effects of Combustion Chamber Structure and Intake Air Humidification on Combustion and Emission Characteristics of Marine Diesel Engine

2017-10-08
2017-01-2254
In order to improve the combustion and emissions for high-speed marine diesel engines, numerical investigations on effects of different combustion chamber structures combined with intake air humidification have to be conducted. The study uses AVL Fire code to establish three-dimensional combustion model and simulate the in-cylinder flow, air-fuel mixing and combustion process with the flow dynamics metrics such as swirl number and uniformity index, analyze the interactional effects of combustion chamber structures and intake air humidification against the experimental data for a part load operation at 1350 r/min, find the optimized way to improve engine performance as well as decrease the NOx and soot emissions. The novelty is that this study is to combine different air humidifying rates with different combustion chamber structures including the re-entrant chamber, the straight chamber and the open chamber.
Technical Paper

Numerical Investigation of the Potential of Late Intake Valve Closing (LIVC) Coupled with Double Diesel Direct-Injection Strategy for Meeting High Fuel Efficiency with Ultra-Low Emissions in a Heavy-Duty Reactivity Controlled Compression Ignition (RCCI) Engine at High Load

2019-04-02
2019-01-1166
The potential of diesel/gasoline RCCI combustion coupled with late intake valve closing (LIVC) and double direct injection of diesel for meeting high fuel efficiency with ultra-low emissions was investigated in this study. The study was aiming at high load operation in a heavy-duty diesel engine. Based on the reactivity stratification of RCCI combustion, the employment of double injection of diesel fuel provided concentration stratification of the high-reactivity fuel, which is to further realize effective control of the combustion process. Meanwhile, late intake valve closing (LIVC) strategy is introduced to control the maximum in-cylinder pressure and nitrogen oxides (NOx) emissions.
Technical Paper

Numerical Analysis of Scavenging Process in a Large Marine Two-Stroke Diesel Engine

2017-10-08
2017-01-2201
For uniflow scavenged two-stroke marine diesel engines, the main function of scavenging process is to replace the burned gas with fresh charge. The end state of scavenging process is integral to the subsequent compression and combustion, thereby affecting the engine’s fuel economy, power output and emissions. In this paper, a complete working cycle of a large marine diesel engine was simulated by using the 3D-CFD software CONVERGE. The model was validated by mesh sensitivity test and experiment data. Based on this calibrated model, the influences of swirl ratio and exhaust valve closing (EVC) timing on the scavenging process were investigated. The parameters evaluating the performance of scavenging process were introduced. The results show that, by adjusting the swirl orientation angle(SOA) from SOA=10° to SOA=30°, different swirl ratios are generated and have obvious differences in flow characteristics and scavenging performance.
Journal Article

Laminar Burning, Combustion and Emission Characteristics of Premixed Methane- Dissociated Methanol-Air Mixtures

2017-03-28
2017-01-1289
This research presents an experimental study of the laminar burning combustion and emission characteristics of premixed methane -dissociated methanol-air mixtures in a constant volume combustion chamber. All experiments were conducted at 3 bar initial pressure and 373K initial temperature. The dissociated methanol fractions were from 20% to 80% with 20% intervals, and the equivalence ratio varied from 0.6 to 1.8 with 0.2 intervals. The images of flame propagation were visualized by using a schlieren system. The combustion pressure data were measured and exhaust emissions were sampled with a portable exhaust gas analyzer. The results show that the unstretched laminar burning velocities increased significantly with dissociated methanol enrichment. The Markstein length decreased with increasing dissociated methanol fraction and decreasing equivalence ratio.
Technical Paper

LES Analysis on Cycle-to-Cycle Variation of Combustion Process in a DISI Engine

2019-01-15
2019-01-0006
Combustion cycle-to-cycle variation (CCV) of Spark-Ignition (SI) engines can be influenced by the cyclic variations in charge motion, trapped mass and mixture composition inside the cylinder. A high CCV leads to misfire or knock, limiting the engine’s operating regime. To understand the mechanism of the effect of flow field and mixture compositions on CCV, the present numerical work was performed in a single cylinder Direct Injection Spark-Ignition (DISI) engine. A large eddy simulation (LES) approach coupled with the G-equation combustion model was developed to capture the CCV by accurately resolving the turbulent flow field spatially and temporally. Further, the ignition process was modeled by sourcing energy during the breakdown and arc phases with a line-shape ignition model which could move with the local flow. Detailed chemistry was solved both inside and outside the flame front. A compact 48-species 152-reactions primary reference fuel (PRF) reduced mechanism was used.
Technical Paper

Knock Threshold Detection in Turbocharged Gasoline Engine Using EEMD and Bispectrum

2016-04-05
2016-01-0643
Knock threshold detection is the key of closed loop control of ignition in gasoline engine, and it is also the difficult point in knock measurement. In this paper, an investigation of knock detection in turbocharged gasoline engine using bispectrum slice and ensemble empirical mode decomposition (EEMD) based on the engine cylinder head vibration signals is presented. By adding some finite amplitude Gaussian white noises to the signal, EEMD keeps the signal continuous in different time span, and therefore the mode mixing inhering in the classical empirical mode decomposition (EMD) method is alleviated. Power spectrum density (PSD) estimation is used to determine the band range of the resonance frequency generated by knock component. EEMD is used to decompose the original signals, the time-frequency characteristics of the Intrinsic Mode Functions (IMF) are analyzed using Continues Wavelet Transform (CWT) due to its excellent time-frequency resolution.
Technical Paper

Investigation on Cylinder Bore Deformation under Static Condition Based on Fourier Decomposition

2017-03-28
2017-01-0366
Due to the mechanical forces under static conditions, the engine cylinders cross section will not be a round circle any more once they are installed. The deformation of an engine cylinder causes increasing lubricating oil consumption and abnormal wear, resulting in worse fuel economy and emissions. However, prediction of deformation on a liner has not been made because of the complication of conditions and structure. In this study, a V6-type engine body model was built and meshed with Hypermesh suit software. Then, cylinder deformation under static condition has been simulated and analyzed. First of all, experimental work was done to verify the engine model. Basically, few parameters like pre-tightened force, structure and distribution of bolts have been investigated to figure out how the cylinder bore deformation behaves via finite element analysis. Also, a simple Matlab program was developed to process the data.
Technical Paper

Fuel Saving Potential of Different Turbo-Compounding Systems Under Steady and Driving Cycles

2015-04-14
2015-01-0878
The performance of three different electric turbo-compounding systems under both steady and driving cycle condition is investigated in this paper. Three configurations studied in this paper are serial turbo-compounding, parallel turbo-compounding and electric assisted turbo-compounding. The electric power, global gain of the whole system (engine and power turbine) under steady operating condition is firstly studied. Then investigation under three different driving cycles is conducted. Items including fuel consumption, engine operating point distribution and transient response performance are analyzed among which the second item is done based on statistic method combined with the results obtained under steady operating conditions. Study under steady condition indicates that electric assisted turbo-compounding system is the best choice compared with the other two systems. The performance of serial turbo-compounding is load oriented while parallel configuration is speed oriented.
Journal Article

Experimental Study on High-Load Extension of Gasoline/PODE Dual-Fuel RCCI Operation Using Late Intake Valve Closing

2017-03-28
2017-01-0754
The dual-fuel Reactivity Controlled Compression Ignition (RCCI) combustion could achieve high efficiency and low emissions over a wide range of operating conditions. However, further high load extension is limited by the excessive pressure rise rate and soot emission. Polyoxymethylene dimethyl ethers (PODE), a novel diesel alternative fuel, has the capability to achieve stoichiometric smoke-free RCCI combustion due to its high oxygen content and unique molecule structure. In this study, experimental investigations on high load extension of gasoline/PODE RCCI operation were conducted using late intake valve closing (LIVC) strategy and intake boosting in a single-cylinder, heavy-duty diesel engine. The experimental results show that the upper load can be effectively extended through boosting and LIVC with gasoline/PODE stoichiometric operation.
Technical Paper

Experimental Study on Combustion Characteristics of Methane/Gasoline Dual-Fuel in a SI Engine at Different Load Conditions

2018-04-03
2018-01-1140
Methane as an attractive alternative fuel offers the most potential in clean combustion and low CO2 emissions. In this work, combustion characteristics of methane/gasoline dual-fuel were investigated in a spark-ignited engine with port-injection of methane and direct-injection of gasoline, allowing for variations in methane addition and excess air coefficient. Engine experimental results showed that under low load conditions, as methane mass rate was raised, there was a promotion in methane/gasoline dual-fuel combustion, and this became more obvious at lean conditions. Similar observations were also obtained when the engine was operated at intermediate load conditions, but a prolonged combustion duration was found with the methane addition. Further analysis showed that the promotion of methane/gasoline dual-fuel combustion with methane addition mainly occurred in the early stage of combustion, especially for lean conditions.
Technical Paper

Experimental Investigation on the Failures of Engine Piston Subjected to Severe Knock

2019-04-02
2019-01-0705
The previous study indicates that the detonation waves generated by acetylene/oxygen mixture can converge in the combustion chamber. In order to verify the destructive effect of detonation wave convergence on piston materials, the detonation bomb device was modified to fundamentally investigate the material failures of aluminum alloy for pistons. The results show that the specimens are destroyed in the middle and edge region after dozens of detonations, which is consistent with the typical characteristics of the piston failures in engines. Therefore, the hypothesis that failures of piston material is caused by the detonation wave convergence is verified.
Technical Paper

Experimental Investigation of Proton Exchange Membrane Fuel Cell with Metal Foam Flow Field

2019-04-02
2019-01-0388
Compared with conventional flow field, metal foam has been increasingly used for gas distributor in the PEM (proton exchange membrane) fuel cell due to its high porosity and conductivity, which significantly enhances the species transport under high current density condition. In this study, the cell performances with metal foam and graphite parallel flow field are compared under normal and subzero temperature conditions. Besides, electrochemical impedance spectroscopy (EIS) is recorded to characterize the Ohmic, polarization and polarization resistance. Under normal condition, the cell with metal foam exhibits three times better performance than the one with parallel flow field. Meanwhile, the effects of inlet gas humidity and flow rates on cell performance are also studied, indicating that the cathode flooding easily occurs due to its difficult water removal. However, the high flow rate can greatly ease the cathode water flooding.
Technical Paper

Experimental Investigation of Combustion and Emission Characteristics of the Direct Injection Dimethyl Ether Enabled Micro-Flame Ignited (MFI) Hybrid Combustion in a 4-Stroke Gasoline Engine

2018-04-03
2018-01-1247
Controlled Auto-Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), has the potential to improve gasoline engines’ efficiency and simultaneously achieve ultra-low NOx emissions. Two of the primary obstacles for applying CAI combustion are the control of combustion phasing and the maximum heat release rate. To solve these problems, dimethyl ether (DME) was directly injected into the cylinder to generate multi-point micro-flame through compression in order to manage the entire heat release of gasoline in the cylinder through port fuel injection, which is known as micro-flame ignited (MFI) hybrid combustion.
Technical Paper

Experimental Investigation of Combustion and Emission Characteristics of Stoichiometric Stratified Flame Ignited (SFI) Hybrid Combustion in a 4-Stroke PFI/DI Gasoline Engine

2019-04-02
2019-01-0960
Controlled Auto-Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), can improve the fuel economy of gasoline engines and simultaneously achieve ultra-low NOx emissions. However, the difficulty in combustion phasing control and violent combustion at high loads limit the commercial application of CAI combustion. To overcome these problems, stratified mixture, which is rich around the central spark plug and lean around the cylinder wall, is formed through port fuel injection and direct injection of gasoline. In this condition, rich mixture is consumed by flame propagation after spark ignition, while the unburned lean mixture auto-ignites due to the increased in-cylinder temperature during flame propagation, i.e., stratified flame ignited (SFI) hybrid combustion.
Technical Paper

Evaluation of Knock Intensity and Knock-Limited Thermal Efficiency of Different Combustion Chambers in Stoichiometric Operation LNG Engine

2019-04-02
2019-01-1137
Liquefied natural gas (LNG) engine could provide both reduced operating cost and reduction of greenhouse gas (GHG) emissions. Stoichiometric operation with EGR and the three-way catalyst has become a potential approach for commercial LNG engines to meet the Euro VI emissions legislation. In the current study, numerical investigations on the knocking tendency of several combustion chambers with different geometries and corresponding performances were conducted using CONVERGE CFD code with G-equation flame propagation model coupled with a reduced natural gas chemical kinetic mechanism. The results showed that the CFD modeling approach could predict the knock phenomenon in LNG engines reasonably well under different thermodynamic and flow field conditions.
Technical Paper

Effects of Lubricating Oil Metallic Content on Morphology, Nanostructure and Graphitization Degree of Diesel Engine Exhaust Particles

2017-03-28
2017-01-1009
In this paper, the influences of metallic content of lubricating oils on diesel particles were investigated. Three lubricating oils with different levels of metallic content were used in a 2.22 Liter, two cylinders, four stroke, and direct injection diesel engine. 4.0 wt. % and 8 wt. % antioxidant and corrosion inhibitor (T202) were added into baseline lubricating oil to improve the performance respectively. Primary particle diameter distributions and particle nanostructure were compared and analyzed by Transmission Electron Microscope. The graphitization degrees of diesel particles from different lubricating oils were analyzed by Raman spectroscopy. Conclusions drawn from the experiments indicate that the metallic content increases the primary particles diameter at 1600 rpm and 2200 rpm. The primary particles diameter ranges from 5 nm to 65 nm and the distribution conformed to Gaussian distribution.
Technical Paper

Effects of Low Temperature Reforming (LTR) Products of Low Octane Number Fuels on HCCI Combustion

2018-09-10
2018-01-1682
In order to achieve high-efficiency and clean combustion in HCCI engines, combustion must be controlled reasonably. A great variety of species with various reactivities can be produced through low temperature oxidation of fuels, which offers possible solutions to the problem of controlling in-cylinder mixture reactivity to accommodate changes in the operating conditions. In this work, in-cylinder combustion characteristics with low temperature reforming (LTR) were investigated in an optical engine fueled with low octane number fuel. LTR was achieved through low temperature oxidation of fuels in a reformer (flow reactor), and then LTR products (oxidation products) were fed into the engine to alter the charge reactivity. Primary Reference Fuels (blended fuel of n-heptane and iso-octane, PRFs) are often used to investigate the effects of octane number on combustion characteristics in engines.
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