Combustion Characteristics of Lean Burn and Stoichiometric With EGR Spark Ignited Natural Gas Engines

2014 ◽  
Author(s):  
Hui Xu ◽  
Leon A. LaPointe
Keyword(s):  
Natural Gas ◽  
Output Power ◽  
Laminar Flame ◽  
Low Cost ◽  
Flame Temperature ◽  
Lean Burn ◽  
Brake Mean Effective Pressure ◽  
Combustion Duration ◽  
Combustion Properties ◽  
Zone Temperature

Natural gas has been widely used in reciprocating engines for various applications such as automobile, electricity generation, and gas compression. It is in the public interest to burn fuels more efficiently and at lower exhaust emissions. Natural gas is very suitable to serve this purpose due to its clean combustion, small carbon footprint, and, with recent breakthroughs in drilling technologies, increased availability and low cost. Natural gas can be used in lean burn spark ignited (LBSI) or stoichiometric EGR spark ignited (SESI) engines. Selection of either LBSI or SESI requires accommodation of requirements such as power output/density, engine efficiency, emissions, knock margin, and cost. The work described in this paper investigated the feasibility of operating an engine originally built as an LBSI under SESI conditions. Analytical tools and workflow developed by Cummins, Inc. are used in this study. The tools require fundamental combustion properties as inputs, including laminar flame speed (LFS), adiabatic flame temperature (AFT) and autoignition interval (AI). These parameters provide critical information about combustion duration, engine out NOx, and relative knock propensity. An existing LBSI engine operating at its as released lambda was selected as baseline. The amount of EGR for the SESI configuration was selected so that it would have the same combustion duration as that of the LBSI at its reference lambda. One dimensional (1D) cycle simulations were conducted under both SESI and LBSI conditions assuming constant output power, compression ratio, volumetric efficiency, heat release centroid and brake mean effective pressure (BMEP). The 1D cycle simulations provide peak cylinder pressure (PCP) and peak unburned zone temperature (PUZT) under LBSI and SESI conditions. The results show that the SESI configuration has lower PCP but higher peak unburned zone temperature than that of the LBSI for the same output power. Also, for the same combustion duration, SESI has higher AFT than that of LBSI, resulting in higher engine out NOx emissions. The SESI configuration has shorter AI than that of LBSI engine, or smaller relative knock margin. Reduction of output power and emissions aftertreatment in the form of a three way catalyst (TWC) is required to operate under SESI engine conditions.

Combustion Characteristics of Lean Burn and Stoichiometric With Exhaust Gas Recirculation Spark-Ignited Natural Gas Engines

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
Hui Xu ◽  
Leon A. LaPointe
Keyword(s):  
Natural Gas ◽  
Output Power ◽  
Flame Temperature ◽  
Exhaust Gas Recirculation ◽  
Exhaust Gas ◽  
Lean Burn ◽  
Brake Mean Effective Pressure ◽  
Combustion Duration ◽  
Combustion Properties ◽  
Gas Recirculation

Natural gas (NG) has been widely used in reciprocating engines for various applications such as automobile, electricity generation, and gas compression. It is in the public interest to burn fuels more efficiently and at lower exhaust emissions. NG is very suitable to serve this purpose due to its clean combustion, small carbon footprint, and, with recent breakthroughs in drilling technologies, increased availability and low cost. NG can be used in lean burn spark-ignited (LBSI) or stoichiometric EGR spark-ignited (SESI) engines. Selection of either LBSI or SESI requires accommodation of requirements such as power output/density, engine efficiency, emissions, knock margin, and cost. The work described in this paper investigated the feasibility of operating an engine originally built as an LBSI under SESI conditions. Analytical tools and workflow developed by Cummins, Inc., are used in this study. The tools require fundamental combustion properties as inputs, including laminar flame speed (LFS), adiabatic flame temperature (AFT), and auto-ignition interval (AI). These parameters provide critical information about combustion duration, engine out NOx, and relative knock propensity. An existing LBSI engine operating at its as released lambda was selected as baseline. The amount of exhaust gas recirculation (EGR) for the SESI configuration was selected so that it would have the same combustion duration as that of the LBSI at its reference lambda. One-dimensional (1D) cycle simulations were conducted under both SESI and LBSI conditions assuming constant output power, compression ratio, volumetric efficiency, heat release centroid, and brake mean effective pressure (BMEP). The 1D cycle simulations provide peak cylinder pressure (PCP) and peak unburned zone temperature (PUZT) under LBSI and SESI conditions. The results show that the SESI configuration has lower PCP but higher PUZT than that of the LBSI for the same output power. Also, for the same combustion duration, SESI has higher AFT than that of LBSI, resulting in higher engine out NOx emissions. The SESI configuration has shorter AI than that of LBSI engine, or smaller relative knock margin. Reduction of output power and emissions aftertreatment in the form of a three-way catalyst (TWC) is required to operate under SESI engine conditions.

Engine Capability Prediction for SI Engine Fueled With Syngas

2015 ◽  
Author(s):  
Hui Xu ◽  
Leon A. LaPointe
Keyword(s):  
Natural Gas ◽  
Solid Waste ◽  
Laminar Flame ◽  
Combustion Engine ◽  
Flame Temperature ◽  
Engine Performance ◽  
Nox Emissions ◽  
Lean Burn ◽  
Gaseous Fuels ◽  
Combustion Duration

There are increasing interests in converting solid waste or lignocellulosic biomass into gaseous fuels and using reciprocating internal combustion engine to generate electricity. A widely used technique is gasification. Gasification is a process where the solid fuel and air are introduced to a partial oxidation environment, and generate combustible gaseous called synthesis gas or syngas. Converting solid waste into gaseous fuel can reduce landfill and create income for process owners. However it can be very challenging to use syngas on a gaseous fueled spark ignited engine, such as a natural gas (NG) engine. NG engines are typically developed with pipeline quality natural gas (PQNG). NG engines can operate at lean burn spark ignited (LBSI), or stoichiometric with EGR spark ignited (SESI) conditions. This work discusses the LBSI engine condition. NG engines can perform very differently when fueled with nonstandard gaseous fuels such as syngas without appropriate tuning. It is necessary to evaluate engine performance in terms of combustion duration, relative knock propensity and NOx emissions for such applications. Due to constraints in time and resources it is often not feasible to test such fuel blends in the laboratory. An analytical method is needed to predict engine performance in a timely manner. This study investigated the possibility of using syngas on a spark ignited engine developed with PQNG. Engine performance was predicted using in house developed models and PQNG as the reference fuel. Laminar flame speed (LFS), adiabatic flame temperature (AFT) and Autoignition interval (AI) are used to predict combustion duration, engine out NOx and engine knock propensity relative to NG at the target Lambda values. Single cylinder research engine data obtained under lean burn conditions fueled with PQNG was selected as the baseline. LFS, AFT and AI of syngas were computed at reference conditions. Lambda of operation was predicted for syngas to provide the same burn rate as NG at the reference Lambda value for NG. Analysis shows that, using syngas at the selected Lambda, the engine can have less engine out NOx emissions and less knock propensity relative to NG at the same speed and load. Modifications to fuel system components may be required to avoid engine derate.

An Alternative Calculation for Methane Number for Lean Burn Spark Ignited Engines Operating on Low Energy Content Gaseous Fuels

2017 ◽  
Author(s):  
Hui Xu ◽  
Axel O. zur Loye ◽  
Robin J. Bremmer
Keyword(s):  
Laminar Flame ◽  
Energy Content ◽  
Flame Temperature ◽  
Relative Difference ◽  
Low Energy ◽  
Si Engine ◽  
Lean Burn ◽  
Combustion Properties ◽  
Si Engines ◽  
Methane Number

Low energy content fuels such as landfill gas can contain a significant amount of diluents like CO2. Critical fuel properties including the lower heating value (LHV) and an anti-knock property, in particular the methane number (MN), should be considered to optimize operation of a spark ignited (SI) engine. The MN has been shown to be a good indicator of knock propensity in stoichiometric SI engines. However, this approach is not always as effective for lean burn SI engines. Two fuels with the same methane number, but with different compositions, may exhibit a different propensity to knocking in an advanced lean burn SI engine. This effect is particularly pronounced when comparing fuels that have different amounts of diluents. In this paper we propose an alternative calculation of the MN, which compensates for the effect of diluents. More specifically, we define a lean burn methane index (LBMI), which is calculated without the diluents. This approach was validated using chemical kinetics modeling. The analysis considered fundamental combustion properties, including laminar flame speed (LFS), adiabatic flame temperature (AFT) and the autoignition interval (AI). For this study, a baseline fuel was selected based on a typical US pipeline natural gas composition. CO2 was then added as a diluent to the baseline fuel to simulate low energy density fuel compositions. Lambda values were selected to provide the same AFT or engine-out NOx. Low energy content fuel were found to have very similar AI values (less than 2% relative difference) to the baseline fuel at the target lambda values. A key result of this study is that the LBMI is a much better predictor of knock propensity than the traditional MN, when comparing fuels with widely varying levels of dilution for advanced lean burn SI engines.

Engine Capability Prediction for Spark Ignited Engine Fueled With Syngas

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Hui Xu ◽  
Leon A. LaPointe
Keyword(s):  
Natural Gas ◽  
Solid Waste ◽  
Combustion Engine ◽  
Flame Temperature ◽  
Engine Performance ◽  
Nox Emissions ◽  
Si Engine ◽  
Lean Burn ◽  
Gaseous Fuels ◽  
Combustion Duration

Abstract There are increasing interests in converting solid waste or lignocellulosic biomass into gaseous fuels and using reciprocating internal combustion engine to generate electricity. A widely used technique is gasification. Gasification is a process where the solid fuel and air are introduced to a partial oxidation environment, and generate combustible gaseous called synthesis gas or syngas. Converting solid waste into gaseous fuel can reduce landfill and create income for process owners. However, it can be very challenging to use syngas on a gaseous fueled spark ignited (SI) engine, such as a natural gas (NG) engine. NG engines are typically developed with pipeline quality natural gas (PQNG). NG engines can operate at lean burn spark ignited (LBSI), or stoichiometric with exhaust gas recirculation (EGR) spark ignited (SESI) conditions. This work discusses the LBSI engine condition. NG engines can perform very differently when fueled with nonstandard gaseous fuels such as syngas without appropriate tuning. It is necessary to evaluate engine performance in terms of combustion duration, relative knock propensity, and NOx emissions for such applications. Due to constraints in time and resources it is often not feasible to test such fuel blends in the laboratory. An analytical method is needed to predict engine performance in a timely manner. This study investigated the possibility of using syngas on an SI engine developed with PQNG. Engine performance was predicted using in house developed models and PQNG as the reference fuel. Laminar flame speed (LFS), adiabatic flame temperature (AFT), and auto-ignition interval (AI) are used to predict combustion duration, engine out NOx and engine knock propensity relative to NG at the target lambda values. Single cylinder research engine data obtained under lean burn conditions fueled with PQNG was selected as the baseline. LFS, AFT, and AI of syngas were computed at reference conditions. Lambda of operation was predicted for syngas to provide the same burn rate as NG at the reference lambda value for NG. Analysis shows that, using syngas at the selected lambda, the engine can have less engine out NOx emissions and less knock propensity relative to NG at the same speed and load. Modifications to fuel system components may be required to avoid engine derate.

scholarly journals The Influence of Diluent Gases on Combustion Properties of Natural Gas: A Combined Experimental and Modeling Study

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Sandra Richter ◽  
Jörn Ermel ◽  
Thomas Kick ◽  
Marina Braun-Unkhoff ◽  
Clemens Naumann ◽  
...  
Keyword(s):  
Power Generation ◽  
Natural Gas ◽  
Laminar Flame ◽  
Ambient Pressure ◽  
Flame Speed ◽  
Laminar Flame Speed ◽  
Diverse Range ◽  
Combustion Properties ◽  
Modeling Study ◽  
A Share

Currently, new concepts for power generation are discussed, as a response to combat global warming due to CO2 emissions stemming from the combustion of fossil fuels. These concepts include new, low-carbon fuels as well as centralized and decentralized solutions. Thus, a more diverse range of fuel supplies will be used, with (biogenic) low-caloric gases such as syngas and coke oven gas (COG) among them. Typical for theses low-caloric gases is the amount of hydrogen, with a share of 50% and even higher. However, hydrogen mixtures have a higher reactivity than natural gas (NG) mixtures, burned mostly in today's gas turbine combustors. Therefore, in the present work, a combined experimental and modeling study of nitrogen-enriched hydrogen–air mixtures, some of them with a share of methane, to be representative for COG, will be discussed focusing on laminar flame speed data as one of the major combustion properties. Measurements were performed in a burner test rig at ambient pressure and at a preheat temperature T0 of 373 K. Flames were stabilized at fuel–air ratios between about φ = 0.5–2.0 depending on the specific fuel–air mixture. This database was used for the validation of four chemical kinetic reaction models, including an in-house one, and by referring to hydrogen-enriched NG mixtures. The measured laminar flame speed data of nitrogen-enriched methane–hydrogen–air mixtures are much smaller than the ones of nitrogen-enriched hydrogen–air mixtures. The grade of agreement between measured and predicted data depends on the type of flames and the type of reaction model as well as of the fuel–air ratio: a good agreement was found in the fuel lean and slightly fuel-rich regime; a large underprediction of the measured data exists at very fuel-rich ratios (φ > 1.4). From the results of the present work, it is obvious that further investigations should focus on highly nitrogen-enriched methane–air mixtures, in particular for very high fuel–air ratio (φ > 1.4). This knowledge will contribute to a more efficient and a more reliable use of low-caloric gases for power generation.

Observation of Flame Propagation in a Heavy-Duty Natural-Gas Lean Burn Spark-Ignition Engine

2019 ◽  
Author(s):  
Jinlong Liu ◽  
Cosmin E. Dumitrescu
Keyword(s):  
Natural Gas ◽  
Flame Propagation ◽  
Low Cost ◽  
Turbulent Flame ◽  
Propagation Speed ◽  
Operating Conditions ◽  
Spark Ignition Engine ◽  
Heavy Duty ◽  
Lean Burn ◽  
Local Flow

Abstract Natural gas (NG) is an alternative combustible fuel for the transportation sectors due to its clean combustion, small carbon footprint, and, with recent breakthroughs in drilling technologies, increased availability and low cost. Currently, NG is better suited for spark-ignited (SI), as a gasoline replacement in conventional SI engines or as a diesel replacement in diesel engines converted to SI operation. However, the knowledge on the fundamentals of NG flame propagation at conditions representative of modern engines (e.g., at higher compression ratios and/or lean mixtures) is limited. Flame propagation inside an engine can be achieved by replacing the original piston with a see-through one. This study visualized flame activities inside the combustion chamber of an optically-accessible heavy-duty diesel engine retrofitted to NG SI operation to increase the understanding of combustion processes inside such converted engines. Recordings of flame luminosity throughout the combustion period at lean-burn operating conditions indicated that the fully-developed turbulent flame formed from several smaller-scale kernels. These small kernels varied with shapes and locations due to different flow motion around the spark location (including the effect of spark electrodes on the local flow separation), different local temperature, or different energy released in these regions. In addition, the turbulent flame was heavily wrinkled during propagation, despite it was grown from a relatively-circular kernel. Moreover, the intake swirl accelerated the flame propagation process while rotating the turbulent flame during its development. Furthermore, the flame propagation speed reduced dramatically when entering the squish region, while the direction from which the flame first touched the bowl edge changed with individual cycles. The results can help the CFD community to better develop RANS and/or LES simulations of such engines under lean-burn operating conditions.

Study of Fuel Composition Effects on Flashback Using a Confined Jet Flame Burner

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Brendan Shaffer ◽  
Zhixuan Duan ◽  
Vincent McDonell
Keyword(s):  
Natural Gas ◽  
Laminar Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Fuel Composition ◽  
Laminar Flame Speed ◽  
Processing Scheme ◽  
High Hydrogen ◽  
Jet Flame ◽  
Wide Range

Flashback is the main operability issue associated with converting lean, premixed combustion systems from operation on natural gas to operation on high hydrogen content fuels. Most syngas fuels contain some amount of hydrogen (15–100%) depending on the fuel processing scheme. With this variability in the composition of syngas, the question of how fuel composition impacts flashback propensity arises. To address this question, a jet burner configuration was used to develop systematic data for a wide range of compositions under turbulent flow conditions. The burner consisted of a quartz burner tube confined by a larger quartz tube. The use of quartz allowed visualization of the flashback processes occurring. Various fuel compositions of hydrogen, carbon monoxide, and natural gas were premixed with air at equivalence ratios corresponding to constant adiabatic flame temperatures (AFT) of 1700 K and 1900 K. Once a flame was stabilized on the burner, the air flow rate would be gradually reduced while holding the AFT constant via the equivalence ratio until flashback occurred. Schlieren and intensified OH* images captured at high speeds during flashback allowed some additional understanding of what is occurring during the highly dynamic process of flashback. Confined and unconfined flashback data were analyzed by comparing data collected in the present study with existing data in the literature. A statistically designed test matrix was used which allows analysis of variance of the results to be carried out, leading to correlation between fuel composition and flame temperature with (1) critical flashback velocity gradient and (2) burner tip temperature. Using the burner tip temperature as the unburned temperature in the laminar flame speed calculations showed increased correlation of the flashback data and laminar flame speed as opposed to when the actual unburned gas temperature was used.

Study of Fuel Composition Effects on Flashback Using a Confined Jet Flame Burner

2012 ◽  
Author(s):  
Brendan Shaffer ◽  
Zhixuan Duan ◽  
Vincent McDonell
Keyword(s):  
Natural Gas ◽  
Laminar Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Fuel Composition ◽  
Laminar Flame Speed ◽  
Processing Scheme ◽  
High Hydrogen ◽  
Jet Flame ◽  
Wide Range

Flashback is the main operability issue associated with converting lean, premixed combustion systems from operation on natural gas to operation on high hydrogen content fuels. Most syngas fuels contain some amount of hydrogen (15–100%) depending on the fuel processing scheme. With this variability in the composition of syngas, the question of how fuel composition impacts flashback propensity arises. To address this question, a jet burner configuration was used to develop systematic data for a wide range of compositions under turbulent flow conditions. The burner consisted of a quartz burner tube confined by a larger quartz tube. The use of quartz allowed visualization of the flashback processes occurring. Various fuel compositions of hydrogen, carbon monoxide, and natural gas were premixed with air at equivalence ratios corresponding to constant adiabatic flame temperatures (AFT) of 1700 K and 1900 K. Once a flame was stabilized on the burner, the air flow rate would be gradually reduced while holding the AFT constant via the equivalence ratio until flashback occurred. Schlieren and intensified OH* images captured at high speeds during flashback allowed some additional understanding of what is occurring during the highly dynamic process of flashback. Confined and unconfined flashback data were analyzed by comparing data collected in the present study with existing data in the literature. A statistically designed test matrix was used which allows analysis of variance of the results to be carried out, leading to correlation between fuel composition and flame temperature with (1) critical flashback velocity gradient and (2) burner tip temperature. Using the burner tip temperature as the unburned temperature in the laminar flame speed calculations showed increased correlation of the flashback data and laminar flame speed as opposed to when the actual unburned gas temperature was used.

Performance and Combustion Investigation of a Lean Burn Natural Gas Engine Using CFD

2018 ◽  
Author(s):  
Sridhar Sahoo ◽  
Srinibas Tripathy ◽  
Dhananjay Kumar Srivastava
Keyword(s):  
Natural Gas ◽  
Equivalence Ratio ◽  
Spark Ignition Engine ◽  
Engine Fuel ◽  
Lean Burn ◽  
Gas Engine ◽  
Natural Gas Engine ◽  
Spark Timing ◽  
Combustion Duration ◽  
Wide Range

Natural gas is widely used in sequentially port fuel injection engine to meet stringent emission regulation. Lean burn operation is one of the ways to improve spark-ignition engine fuel economy. The instability in the combustion process of the lean burn engine is one of the major challenges for engine research. In this study, the performance and combustion characteristics of a lean burn sequential injection compressed natural gas (CNG) engine were investigated numerically using computational fluid dynamics (CFD) modeling over a wide range of air/fuel equivalence ratio. A detailed chemical kinetic mechanism was used for natural gas combustion along with laminar flame speed model to capture lean burn operating condition within the combustion chamber. Combustion pressure, indicated mean effective pressure (IMEP), and heat release were analyzed for performance analysis, whereas flame development angle (CA 10), combustion duration, thermal efficiency were taken for combustion analysis. The results show that on increasing air/fuel equivalence ratio at a given spark timing, IMEP decreases as the lean burn mixture produces less amount of gross power output due to insufficient available energy. Moreover, lower burning velocity characteristic of natural gas extends the combustion duration, where a substantial amount of total energy released after top dead center. It is also seen that optimum spark timing (MBT) for maximum IMEP advances with an increase in air/fuel equivalence ratio due to late ignition timing under lean burn condition. CFD model successfully captures the effect of dilution to illustrate the considerations to design future combustion engine for spark ignited natural gas engine.

Phenomenological Analysis of Combustion of Gaseous Fuels to Measure the Energy Quality and the Capacity to Produce Work in Spark Ignition Engines.

2020 ◽  
Author(s):  
Juan Pablo GOMEZ MONTOYA ◽  
Andres Amell
Keyword(s):  
Energy Density ◽  
Compression Ratio ◽  
Laminar Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Laminar Flame Speed ◽  
Adiabatic Flame Temperature ◽  
Gaseous Fuels ◽  
Combustion Properties ◽  
Si Engines

Abstract Combustion at the knocking threshold was tested using fuels with different methane numbers (MN) in a modified SI engine, with high compression ratio (CR) and high turbulence intensity to the combustion process; fuels were tested in a CFR engine to measure MN and critical compression ratio (CCR); in both engines test were performed just into the knocking threshold. Is proposed that MN to gaseous fuels will be considered in similar way than octane number (ON) to liquid fuels to indicate the energy quality and the capacity to produce work. According to the tests biogas has better combustion properties than the others fuels; biogas is the fuel with the highest knocking resistance; biogas is the fuel with the best energy quality measured with the energy density and combustion temperature; biogas has the highest capacity to produce work in SI engines, because its high MN, low energy density, low laminar flame speed and low adiabatic flame temperature. Fuel combustion phenomenological characteristics were compared using CCR versus: output power, generating efficiency, energy density, laminar flame speed and adiabatic flame temperature. It is suggested that the strategies to suppress knocking are the key to improve the performance of SI engines; knocking is the engine limit to power generation in SI engines and quantum thermal efficiency is defined at this condition.

Sign in / Sign up

Export Citation Format

Share Document