scholarly journals Control and optimization of spark ignition–controlled auto-ignition hybrid combustion based on stratified flame ignition

2018 ◽  
Vol 233 (12) ◽  
pp. 3057-3073 ◽  
Author(s):  
Tao Chen ◽  
Xinyan Wang ◽  
Hua Zhao ◽  
Hui Xie ◽  
Bangquan He
Keyword(s):  
Heat Release ◽  
Flame Propagation ◽  
Thermal Efficiency ◽  
Direct Injection ◽  
Combustion Process ◽  
Spark Ignition ◽  
Release Process ◽  
Auto Ignition ◽  
Flame Ignition ◽  
Injection Ratio

Spark ignition–controlled auto-ignition hybrid combustion, also known as spark assisted compression ignition, is of considerable interest in gasoline engines because of its potential to enlarge the operating range of gasoline diluted combustion. However, it was found that the spark ignition–controlled auto-ignition hybrid combustion process was often characterized with large cycle-to-cycle variations. In this research, a new approach by combining the traditional second-order derivative method and Wiebe function fitting method was proposed to identify different heat release stages of spark ignition–controlled auto-ignition hybrid combustion. The heat release characteristics of the spark ignition–controlled auto-ignition hybrid combustion based on stratified flame ignition strategy and its control methods were investigated in detail. The effect of control parameters, including spark timing, direct injection ratio and dilution strategy, on improving the thermal efficiency and decreasing the variation of heat release trace in spark ignition–controlled auto-ignition hybrid combustion based on stratified flame ignition strategy was analysed. The advance of flame propagation ending point and the increase in the average heat release rate in flame propagation stage benefitted the fuel economy and reduced the variations of heat release in spark ignition–controlled auto-ignition hybrid combustion. Although the increase in direct injection ratio contributed to the stability of heat release in the spark ignition–controlled auto-ignition hybrid combustion based on the stratified flame ignition strategy, the thermal efficiency of spark ignition–controlled auto-ignition hybrid combustion cannot be effectively optimized due to the decrease in combustion efficiency. The application of exhaust gas recirculation and air dilution could decrease the variations of heat release process and increase the thermal efficiency of spark ignition–controlled auto-ignition hybrid combustion based on stratified flame ignition strategy.

The comparison between traditional spark ignition and micro flame ignition in gasoline high dilution combustion

2021 ◽  
pp. 095440702098316
Author(s):  
Yifang Feng ◽  
Tao Chen ◽  
Kang Xu ◽  
Xinyan Wang ◽  
Hui Xie ◽  
...  
Keyword(s):  
Heat Release ◽  
Flame Propagation ◽  
High Efficiency ◽  
Combustion Process ◽  
Spark Ignition ◽  
Low Temperature Combustion ◽  
Reaction Fronts ◽  
Auto Ignition ◽  
Flame Ignition ◽  
Operational Range

Gasoline spark ignition (SI) – Controlled auto-ignition (CAI) hybrid combustion had previously been shown to expanding the operational range of high-efficiency low-temperature combustion and reducing fuel consumption. However, the spark ignition became ineffective when the mixture became highly diluted and the large cyclic variation and even misfire would occur. To achieve high-efficiency combustion in extended engine operational range and overcome the limitation of SI-CAI hybrid combustion, Micro Flame Ignition (MFI) was proposed and researched as a mean to providing multiple auto-ignition sites to initiate the combustion process of the diluted mixture. In this research, both engine experiments and Computational Fluid Dynamics (CFD) simulations were carried out to study the MFI combustion and SI-CAI hybrid combustion in a single-cylinder optical engine. Compared to the SI-CAI hybrid combustion, the flame propagation in MFI hybrid combustion was initiated by a large number of reaction fronts produced by the DME auto-ignition at multiple sites. MFI was found to deliver substantially more heat and ignition energy to the premixed mixture than the single spark ignition, enabling much faster initial heat release. However, the flame front expansion speed of MFI hybrid combustion dropped significantly to a similar value to that of the SI-CAI case because of the slower flame speed of diluted gasoline mixture. The MFI combustion exhibited three phases of autoignition stage, flame propagation stage and fast heat release stage. It is characterized by a higher peak heat release rate and shorter duration of the main combustion than those of the SI-CAI combustion. Besides, the use of spark ignition in the MFI operation promoted the autoignition of DME, leading to a shorter combustion duration and faster combustion than the MFI combustion without spark ignition. As a result, the spark assisted MFI strategy could be used to control the combustion phasing and optimize the MFI combustion process.

Numerical Investigation of Fuel Property Effects on Mixed-Mode Combustion in a Spark-Ignition Engine

2019 ◽  
Author(s):  
Chao Xu ◽  
Pinaki Pal ◽  
Xiao Ren ◽  
Sibendu Som ◽  
Magnus Sjöberg ◽  
...  
Keyword(s):  
Heat Release ◽  
Flame Propagation ◽  
Heat Release Rate ◽  
Release Rate ◽  
Octane Number ◽  
Mixed Mode ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Chemical Effect ◽  
Auto Ignition

Abstract In the present study, mixed-mode combustion of an E30 fuel in a direct-injection spark-ignition engine is numerically investigated at a fuel-lean operating condition using multidimensional computational fluid dynamics (CFD). A fuel surrogate matching Research Octane Number (RON) and Motor Octane Number (MON) of E30 is first developed using neural network based non-linear regression model. To enable efficient 3D engine simulations, a 164-species skeletal reaction mechanism incorporating NOx chemistry is reduced from a detailed chemical kinetic model. A hybrid approach that incorporates the G-equation model for tracking turbulent flame front, and the multi-zone well-stirred reactor model for predicting auto-ignition in the end gas, is employed to account for turbulent combustion interactions in the engine cylinder. Predicted in-cylinder pressure and heat release rate traces agree well with experimental measurements. The proposed modelling approach also captures moderated cyclic variability. Two different types of combustion cycles, corresponding to purely deflagrative and mixed-mode combustion, are observed. In contrast to the purely deflagrative cycles, mixed-mode combustion cycles feature early flame propagation followed by end-gas auto-ignition, leading to two distinctive peaks in heat release rate traces. The positive correlation between mixed-mode combustion cycles and early flame propagation is well captured by simulations. With the validated numerical setup, effects of NOx chemistry on mixed-mode combustion predictions are investigated. NOx chemistry is found to promote auto-ignition through residual gas recirculation, while the deflagrative flame propagation phase remains largely unaffected. Local sensitivity analysis is then performed to understand effects of physical and chemical properties of the fuel, i.e., heat of evaporation (HoV) and laminar flame speed (SL). An increased HoV tends to suppress end-gas auto-ignition due to increased vaporization cooling, while the impact of HoV on flame propagation is insignificant. In contrast, an increased SL is found to significantly promote both flame propagation and auto-ignition. The promoting effect of SL on auto-ignition is not a direct chemical effect; it is rather caused by an advancement of the combustion phasing, which increases compression heating of the end gas.

Numerical study of the effect of split direct injection on the lean-burn combustion characteristics in a poppet-valve two-stroke gasoline engine at high loads

2020 ◽  
pp. 146808742093240
Author(s):  
Xiao Li ◽  
Bang-Quan He ◽  
Hua Zhao
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Thermal Efficiency ◽  
Direct Injection ◽  
Lean Burn ◽  
Gasoline Engines ◽  
Poppet Valve ◽  
Auto Ignition ◽  
Second Peak

Poppet-valve two-stroke gasoline engines can increase specific power of four-stroke gasoline engines with the same displacement. But knocking combustion may also occur at high loads in two-stroke engines. The application of stratified lean-burn on poppet-valve two-stroke gasoline engines can avoid knocking and increase combustion stability. To investigate the effect of the mixture stratification on lean-burn events at high loads, simulation was conducted in different split direct injection conditions with constant fuel mass when equivalence ratio is 0.625. Results show that most fuel distributes near the center of the cylinder at any second direct injection ratio ( rSOI2). At different rSOI2s, auto-ignition occurs during flame propagation, causing shortened combustion duration. Auto-ignition causes the second peak of the heat release rate. The second peak of the heat release rate first decreases and then increases with increased rSOI2. Indicated mean effective pressure and indicated thermal efficiency increase with increased maximum pressure rise rate. The maximum indicated thermal efficiency of 42% can be reached without knocking combustion at 1500 rpm. The proportion of fuel mass through auto-ignition in the cylinder is an important factor to change the indicated thermal efficiency of a lean-burn engine at high loads.

Twin-Peak Heat Release Phenomenon Inside a Heavy-Duty Diesel Engine Retrofitted to Natural-Gas Spark Ignition

2019 ◽  
Author(s):  
Jinlong Liu ◽  
Cosmin E. Dumitrescu ◽  
Christopher Ulishney
Keyword(s):  
Diesel Engine ◽  
Natural Gas ◽  
Heat Release ◽  
Energy Release ◽  
Flame Propagation ◽  
Combustion Process ◽  
Spark Ignition ◽  
Operating Conditions ◽  
Heavy Duty ◽  
Double Peak

Abstract Existing compression ignition engines can be modified to spark ignition configuration to increase the use of natural gas in the heavy-duty transportation sector. A better understanding of the premixed natural gas combustion inside the original diesel chamber (i.e., flat-head-and-bowl-in-piston) will help improve the conversion process and therefore accelerate the diesel engine conversion. Previous studies indicated that the burning process in such engines is a two-stage combustion with a fast burning inside the bowl and a slower burning inside the squish. This paper used experimental and numerical results to investigate the combustion process at a more advanced spark timing representative of ultra-lean medium-load operation, which placed most of the combustion inside the compression stroke. At such operating conditions, the high turbulence intensity inside the squish region accelerated the flame propagation inside the squish region to the point that the burn inside the bowl separated less from that inside the squish region. However, several individual cycles produced a double-peak energy-release with the peak locations closer to the only one heat release peak seen in the average cycle. Moreover, RANS CFD simulations indicated that the time at which the flame entered the squish region was near the peak location of the energy-release process for the conditions investigated here. As a result, the data suggests that the double-peak seen in the apparent heat release rate was the result of the cycle-by-cycle variation in the flame propagation.

Combustion development in a gasoline-fueled spark ignition–controlled auto-ignition engine operated at different spark timings and intake air temperatures

2019 ◽  
pp. 146808741989416
Author(s):  
Melih Yıldız ◽  
Bilge Albayrak Çeper
Keyword(s):  
Flame Propagation ◽  
Mass Fraction ◽  
Transition Point ◽  
Combustion Process ◽  
Spark Ignition ◽  
Engine Operation ◽  
Air Temperatures ◽  
Auto Ignition ◽  
Crank Angle ◽  
Flame Development

Spark ignition–controlled auto-ignition is a combustion strategy to overcome the challenges in a homogeneous charge compression ignition or controlled auto-ignition combustion which has a limited operation region and does not have any direct control of the combustion timing. However, the spark ignition–controlled auto-ignition combustion can result in a large cyclic variability due to two main distinctive combustion phases developing initially by flame propagation and following controlled auto-ignition combustion throughout an engine cycle. Characterization of combustion development is, therefore, required to maintain a stable engine operation under spark ignition–controlled auto-ignition combustion. In this research, experimental studies were carried out to investigate spark ignition–controlled auto-ignition combustion development at different spark advances and intake air temperatures. Combustion analyses were performed employing pressure-based heat release and mass fraction burn curve to determine the main combustion parameters along with transition points (corresponding to crank angles) to controlled auto-ignition and mass fraction burnt by flame propagation. The results reveal that transition point has a strong correlation with crank angle position where 10% of fuel mass consumed combustion phasing rather than mass fraction burnt by flame propagation at the same intake air temperature. The cycles with a higher mass fraction burnt by flame propagation can result from early flame development at the advanced spark timings (at −30 and −40 °CA) while the slow flame development at a spark timing of −20 °CA due to late transition point corresponding to crank angle occurred. Besides, it is also found that flame propagation phase more contributes to the cyclic variation in the whole combustion process.

scholarly journals The Effect of RME-1-Butanol Blends on Combustion, Performance and Emission of a Direct Injection Diesel Engine

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2941
Author(s):  
Wojciech Tutak ◽  
Arkadiusz Jamrozik ◽  
Karol Grab-Rogaliński
Keyword(s):  
Diesel Engine ◽  
Heat Release ◽  
Direct Injection ◽  
Specific Energy Consumption ◽  
Combustion Process ◽  
Constant Load ◽  
Combustion Stability ◽  
Performance And Emission ◽  
Energy Share ◽  
The Stability

The main objective of this study was assessment of the performance, emissions and combustion characteristics of a diesel engine using RME–1-butanol blends. In assessing the combustion process, great importance was placed on evaluating the stability of this process. Not only were the typical COVIMEP indicators assessed, but also the non-burnability of the characteristic combustion stages: ignition delay, time of 50% heat release and the end of combustion. The evaluation of the combustion process based on the analysis of heat release. The tests carried out on a 1-cylinder diesel engine operating at a constant load. Research and evaluation of the combustion process of a mixture of RME and 1-butanol carried out for the entire range of shares of both fuels up to 90% of 1-butanol energetic fraction. The participation of butanol in combustion process with RME increased the in-cylinder peak pressure and the heat release rate. With the increase in the share of butanol there was noted a decrease in specific energy consumption and an increase in engine efficiency. The share of butanol improved the combustion stability. There was also an increase in NOx emissions and decrease in CO and soot emissions. The engine can be power by blend up to 80% energy share of butanol.

scholarly journals Combustion Thermodynamics of Ethanol, n-Heptane, and n-Butanol in a Rapid Compression Machine with a Dual Direct Injection (DDI) Supply System

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2729
Author(s):  
Ireneusz Pielecha ◽  
Sławomir Wierzbicki ◽  
Maciej Sidorowicz ◽  
Dariusz Pietras
Keyword(s):  
Heat Release ◽  
Combustion Chamber ◽  
Internal Combustion Engines ◽  
Direct Injection ◽  
Combustion Process ◽  
Combustion Efficiency ◽  
Injection System ◽  
Rapid Compression Machine ◽  
Process Indicators ◽  
Rapid Compression

The development of internal combustion engines involves various new solutions, one of which is the use of dual-fuel systems. The diversity of technological solutions being developed determines the efficiency of such systems, as well as the possibility of reducing the emission of carbon dioxide and exhaust components into the atmosphere. An innovative double direct injection system was used as a method for forming a mixture in the combustion chamber. The tests were carried out with the use of gasoline, ethanol, n-heptane, and n-butanol during combustion in a model test engine—the rapid compression machine (RCM). The analyzed combustion process indicators included the cylinder pressure, pressure increase rate, heat release rate, and heat release value. Optical tests of the combustion process made it possible to analyze the flame development in the observed area of the combustion chamber. The conducted research and analyses resulted in the observation that it is possible to control the excess air ratio in the direct vicinity of the spark plug just before ignition. Such possibilities occur as a result of the properties of the injected fuels, which include different amounts of air required for their stoichiometric combustion. The studies of the combustion process have shown that the combustible mixtures consisting of gasoline with another fuel are characterized by greater combustion efficiency than the mixtures composed of only a single fuel type, and that the influence of the type of fuel used is significant for the combustion process and its indicator values.

G-equation based ignition model for direct injection spark ignition engines

2021 ◽  
pp. 146808742110139
Author(s):  
Arun C Ravindran ◽  
Sage L Kokjohn ◽  
Benjamin Petersen
Keyword(s):  
Heat Release ◽  
Direct Injection ◽  
Turbulent Flame ◽  
Spark Ignition ◽  
Discharge Process ◽  
Flame Kernel ◽  
Turbulent Flame Speed ◽  
Direct Injection Spark Ignition ◽  
Kernel Growth ◽  
Spark Energy

To accurately model the Direct Injection Spark Ignition (DISI) combustion process, it is important to account for the effects of the spark energy discharge process. The proximity of the injected fuel spray and spark electrodes leads to steep gradients in local velocities and equivalence ratios, particularly under cold-start conditions when multiple injection strategies are employed. The variations in the local properties at the spark plug location play a significant role in the growth of the initial flame kernel established by the spark and its subsequent evolution into a turbulent flame. In the present work, an ignition model is presented that is compatible with the G-Equation combustion model, which responds to the effects of spark energy discharge and the associated plasma expansion effects. The model is referred to as the Plasma Velocity on G-surface (PVG) model, and it uses the G-surface to capture the early kernel growth. The model derives its theory from the Discrete Particle Ignition (DPIK) model, which accounts for the effects of electrode heat transfer, spark energy, and chemical heat release from the fuel on the early flame kernel growth. The local turbulent flame speed has been calculated based on the instantaneous location of the flame kernel on the Borghi-Peters regime diagram. The model has been validated against the experimental measurements given by Maly and Vogel,1 and the constant volume flame growth measurements provided by Nwagwe et al.2 Multi-cycle simulations were performed in CONVERGE3 using the PVG ignition model in combination with the G-Equation-based GLR4 model in a RANS framework to capture the combustion characteristics of a DISI engine. Good agreements with the experimental pressure trace and apparent heat-release rates were obtained. Additionally, the PVG ignition model was observed to substantially reduce the sensitivity of the default G-sourcing ignition method employed by CONVERGE.

scholarly journals LES study on mixing and combustion in a Direct Injection Spark Ignition engine

2018 ◽  
Vol 73 ◽  
pp. 32
Author(s):  
Nicolas Iafrate ◽  
Anthony Robert ◽  
Jean-Baptiste Michel ◽  
Olivier Colin ◽  
Benedicte Cuenot ◽  
...  
Keyword(s):  
Ignition Time ◽  
Direct Injection ◽  
Combustion Process ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Pollutant Emissions ◽  
Spark Ignition Engines ◽  
Eddy Simulation ◽  
Mixture Preparation ◽  
The Impact

Downsized spark ignition engines coupled with a direct injection strategy are more and more attractive for car manufacturers in order to reduce pollutant emissions and increase efficiency. However, the combustion process may be affected by local heterogeneities caused by the interaction between the spray and turbulence. The aim for car manufacturers of such engine strategy is to create, for mid-to-high speeds and mid-up-high loads, a mixture which is as homogeneous as possible. However, although injection occurs during the intake phase, which favors homogeneous mixing, local heterogeneities of the equivalence ratio are still observed at the ignition time. The analysis of the mixture preparation is difficult to perform experimentally because of limited optical accesses. In this context, numerical simulation, and in particular Large Eddy Simulation (LES) are complementary tools for the understanding and analysis of unsteady phenomena. The paper presents the LES study of the impact of direct injection on the mixture preparation and combustion in a spark ignition engine. Numerical simulations are validated by comparing LES results with experimental data previously obtained at IFPEN. Two main analyses are performed. The first one focuses on the fuel mixing and the second one concerns the effect of the liquid phase on the combustion process. To highlight these phenomena, simulations with and without liquid injection are performed and compared.

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