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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

Dilution Boundary Expansion Mechanism of SI-CAI Hybrid Combustion Based on Micro Flame Ignition Strategy

2019-04-02
2019-01-0954
In decade years, Spark Ignition-Controlled Auto Ignition (SI-CAI) hybrid combustion, also called Spark Assisted Compression Ignition (SACI) has shown its high-efficiency and low emissions advantages. However, high dilution causes the problem of unstable initial ignition and flame propagation, which leads to high cyclic variation of heat release and IMEP. The instability of SI-CAI hybrid combustion limits its dilution degree and its ability to improve the thermal efficiency. In order to solve instability problems and expand the dilution boundary of hybrid combustion, micro flame ignition (MFI) strategy is applied in gasoline hybrid combustion engines. Small amount of Dimethyl Ether (DME) chosen as the ignition fuel is injected into cylinder to form micro flame kernel, which can stabilize the ignition combustion process.
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 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

Surface Functional Groups and Graphitization Degree of Soot in the Sooting History of Methane Premixed Flame

2017-03-28
2017-01-1003
The evolution of surface functional groups (SFGs) and the graphitization degree of soot generated in premixed methane flames are studied and the correlation between them is discussed. Test soot samples were obtained from an optimized thermophoretic sampling system and probe sampling system. The SFGs of soot were determined by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) after removing the soluble impurities from the soot samples, while the graphitization degree of soot was characterized by Raman spectrum and electron energy loss spectroscopy (EELS). The results reveal that the number of aliphatic C-H groups and C=O groups shows an initial increase and then decrease in the sooting history. The large amount of aliphatic C-H groups and small amount of aromatic C-H groups in the early stage of the soot mass growth process indicate that aliphatic C-H groups make a major contribution to the early stage of soot mass growth.
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.
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

A Comparative Study on the Fuel Economy Improvement of a Natural Gas SI Engine at the Lean Burn and the Stoichiometric Operation both with EGR under the Premise of Meeting EU6 Emission Legislation

2015-09-01
2015-01-1958
In order to further study the effects of air and EGR dilution on the fuel economy improvement of natural gas engines under the premise of meeting EU6 legislation, a comparison between stoichiometric operation with EGR and lean burn operation with and without EGR has been conducted at 1600rpm 50% and 75% load. The conversion efficiencies of the catalysts for both NOx and CH4 emissions are assumed at 90% for lean burn operation. Experiment results indicate that under the condition of meeting both NOx and CH4 predetermined engine-out emissions limits for EU6 legislation, lean operation with a small fraction of EGR dilution enables more advanced combustion phasing compared to pure lean operation, which results in much better fuel economy, thus further improvement compared to stoichiometric operation is achieved.
Technical Paper

Organic Compound Exhaust Analysis from Ethanol-Gasoline Fueled Motorcycle

2005-10-12
2005-32-0055
Ethanol-Gasoline was being promoted in China. Ethanol as substitute fuel could save such nature resource that cannot be regenerated. At the same time, oxygen additives also have potential dangerous, such as, poisonous organic compound. In this paper, a typical 125 mL four stroke single cylinder motorcycle was driven on chassis dynamometer at 5 different stable conditions which is specified in ECE 40 driving cycle. At each stably driving condition, raw gas from exhaust pipe was collected in corresponding bags respectively. Those samples were analyzed by means of gas chromatogram and mass spectrum analyzer (Agilent GC6890-MS5973). Poisonous ethanol compound such as benzene, toluene had been found in samples from ethanol blended fueled motorcycle exhausts and compared with samples from that of pure gasoline.
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