Fuel Stratification Using Twin-Tumble Intake Flows to Extend Lean Limit in Super-Lean Gasoline Combustion

2018 ◽  
Author(s):  
Yasuo Moriyoshi ◽  
Tatsuya Kuboyama ◽  
Makoto Kaneko ◽  
Toshio Yamada ◽  
Hironao Sato
Keyword(s):  
Fuel Stratification ◽  
Lean Limit ◽  
Lean Gasoline

scholarly journals Optical Investigation of a Partial Fuel Stratification Strategy to Stabilize Overall Lean Operation of a DISI Engine Fueled with Gasoline and E30

Energies ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 396
Author(s):  
Cinzia Tornatore ◽  
Magnus Sjöberg
Keyword(s):  
Volume Fraction ◽  
Direct Injection ◽  
Combustion Process ◽  
Pilot Injection ◽  
Optical Investigation ◽  
Flame Kernel ◽  
Lean Combustion ◽  
Fuel Stratification ◽  
Spark Plug ◽  
Initial Flame

This paper offers new insights into a partial fuel stratification (PFS) combustion strategy that has proven to be effective at stabilizing overall lean combustion in direct injection spark ignition engines. To this aim, high spatial and temporal resolution optical diagnostics were applied in an optically accessible engine working in PFS mode for two fuels and two different durations of pilot injection at the time of spark: 210 µs and 330 µs for E30 (gasoline blended with ethanol by 30% volume fraction) and gasoline, respectively. In both conditions, early injections during the intake stroke were used to generate a well-mixed lean background. The results were compared to rich, stoichiometric and lean well-mixed combustion with different spark timings. In the PFS combustion process, it was possible to detect a non-spherical and highly wrinkled blue flame, coupled with yellow diffusive flames due to the combustion of rich zones near the spark plug. The initial flame spread for both PFS cases was faster compared to any of the well-mixed cases (lean, stoichiometric and rich), suggesting that the flame propagation for PFS is enhanced by both enrichment and enhanced local turbulence caused by the pilot injection. Different spray evolutions for the two pilot injection durations were found to strongly influence the flame kernel inception and propagation. PFS with pilot durations of 210 µs and 330 µs showed some differences in terms of shapes of the flame front and in terms of extension of diffusive flames. Yet, both cases were highly repeatable.

Fuel Stratification in a Liquid-Phase LPG Injection Engine

2003 ◽  
Author(s):  
Seungmook Oh ◽  
Yonggyu Lee ◽  
Kernyong Kang ◽  
Youngmin Woo ◽  
Choongsik Bae
Keyword(s):  
Liquid Phase ◽  
Fuel Stratification

Identification of the extinction mechanism of lean limit hydrogen flames based on Lewis number effect

2021 ◽  
Vol 174 ◽  
pp. 121288
Author(s):  
Joongoo Jeon ◽  
Doyoung Shin ◽  
Wonjun Choi ◽  
Sung Joong Kim
Keyword(s):  
Lewis Number ◽  
Lean Limit

A Quasi-Dimensional Fuel Distribution Model for a Radially Stratified Engine

2021 ◽  
Author(s):  
Dennis Robertson ◽  
Patrick O'Donnell ◽  
Benjamin Lawler ◽  
Robert Prucka
Keyword(s):  
Reference Model ◽  
Computation Time ◽  
Distribution Model ◽  
Strategy Development ◽  
Real Time Control ◽  
Spray Penetration ◽  
Fuel Distribution ◽  
Time Control ◽  
Fuel Stratification ◽  
Execution Speed

Abstract Several combustion strategies leverage radial fuel stratification to adapt combustion performance between the center of the chamber and the outer regions independently. Spark-assisted compression ignition (SACI) relies on careful tuning of this radial stratification to maximize the combined performance of flame propagation and autoignition. Established techniques for determining in-cylinder fuel stratification are computationally intensive, limiting their feasibility for control strategy development and real-time control. A simplified model for radial fuel stratification is developed for control-oriented objectives. The model consists of three submodels: spray penetration, fuel distribution along the spray axis, and post-injection mixing. The spray penetration model is adapted from fuel spray models presented in the literature. The fuel distribution and mixing submodels are validated against injection spray results from an LES 3-D computational fluid dynamics (CFD) reference model for three test points as a function of crank angle. The quasi-one-dimensional model matches the CFD results with a root mean square error (RMSE) for equivalence ratio of 0.08?0.11. This is a 50% reduction from the 0.16?0.20 RMSE for a model that assumes a uniform fuel distribution immediately after injection. The computation time is 230 ms on an Intel Xeon E5-1620 v3 to solve each case without significant optimization for code execution speed.

Ignition System Designed to Extend the Plug Life, and the Lean Limit in a Natural Gas Engine

2003 ◽  
Author(s):  
A. K. Chan ◽  
S. H. Waters
Keyword(s):  
Natural Gas ◽  
Engine Performance ◽  
Ignition System ◽  
Gas Engine ◽  
Natural Gas Engine ◽  
Dc System ◽  
Spark Plug ◽  
Long Duration ◽  
Discharge Duration ◽  
Lean Limit

An ignition system that is based on the alternating (AC) rather than the traditional direct (DC) current in the spark plug discharge has been developed at the Caterpillar Technical Center. This system can generate a long duration discharge with controllable power. It is believed that such an ignition system can provide both a leaner operating limit and a longer spark plug life than a traditional DC system due to the long discharge duration and the low discharge power. The AC ignition system has successfully been tested on a Caterpillar single cylinder G3500 natural gas engine to determine the effects on the engine performance, combustion characteristics and emissions. The test results indicate that while the AC ignition system has only a small impact on engine performance (with respect to a traditional DC system), it does extend the lean limit with lower NOx emissions. Evidences also show the potential of reduce spark plug electrode erosions from the low breakdown and sustaining discharge powers from the AC ignition system. This paper summarizes the prototype design and engine demonstration results of the AC ignition system.

scholarly journals Direct Measurement of Ammonia Storage on Passive SCR Systems for Lean Gasoline NOx Reduction Using Radio Frequency Sensing

2019 ◽  
Author(s):  
Paul Ragaller ◽  
Josh Mandelbaum ◽  
Luc Lapenta ◽  
Alexander Sappok ◽  
Josh Pihl ◽  
...  
Keyword(s):  
Radio Frequency ◽  
Real Time ◽  
Gasoline Engine ◽  
Nox Reduction ◽  
Practical Implementation ◽  
Engine Operation ◽  
Ammonia Storage ◽  
Scr System ◽  
Lean Gasoline ◽  
Passive Scr

Abstract Lean gasoline engine operation provides clear efficiency benefits relative to conventional stoichiometric combustion approaches. One of the key hurdles to the widespread, practical implementation of lean gasoline combustion remains the challenge of lean NOx control. One of the potential approaches for controlling NOx emission from lean gasoline engines is the so-called passive selective catalytic reduction (SCR) system. In such systems, periods of rich operation generate ammonia over a three-way catalyst (TWC), which is then adsorbed on the downstream SCR and consumed during lean operation. Brief periods of rich operation must occur in response to the depletion of stored ammonia on the SCR, which requires reliable measurements of the SCR ammonia inventory. Presently, lean exhaust system controls rely on a variety of gas sensors mounted up- and downstream of the catalysts, and which only provide an indirect inference of the operation state. In this study, a radio frequency (RF) sensor was used to provide a direction measurement of the amount of ammonia adsorbed on the SCR in real-time. The RF sensor was calibrated and deployed on a BMW N43B20 4-cylinder lean gasoline engine equipped with a passive SCR system. Brief periods of rich operation performed at lambda values between 0.98 and 0.99 generated the ammonia, subsequently stored on the SCR for consumption during periods of lean operation. The experiments compared real-time measurements of SCR ammonia inventory from the RF sensor with estimates of ammonia coverage derived from exhaust gas composition measurements upstream and downstream of the catalyst. The results showed a high degree of correlation between the RF measurements and SCR ammonia storage inventory, and demonstrated NOx conversion efficiencies above 98%, confirming the feasibility of the concept. Relative to stoichiometric operation, lean-gasoline operation resulted in fuel efficiency gains of up to 10%, which may be further improved through direct feedback control from the RF sensor to optimize lean–rich cycling based on actual, measured SCR ammonia levels.

Fuel Injection Control for a Valve Array in a Shockless Explosion Combustor

2018 ◽  
Author(s):  
Jan-Simon Schäpel ◽  
Rudibert King ◽  
Fatma Yücel ◽  
Fabian Völzke ◽  
Christian Oliver Paschereit ◽  
...  
Keyword(s):  
Fuel Injection ◽  
Combustion Process ◽  
Firing Frequency ◽  
Mixed Integer ◽  
Test Rig ◽  
Proportional Valve ◽  
Control Approach ◽  
Fuel Stratification ◽  
Auto Ignition ◽  
Filling Time

Approximate constant volume combustion (aCVC) is a promising way to optimize the combustion process in a gas turbine, which would exceed the gain in efficiency resulting from optimizing other components significantly. This work deals with a recently proposed approach: shockless explosion combustion (SEC). Compared to already known concepts, such as pulsed detonation combustion (PDC), it overcomes several disadvantages, e.g., sharp pressure transitions and entropy generation due to shock waves. For an SEC, accurate fuel stratification is required to achieve a quasi-homogeneous auto-ignition. In an atmospheric test rig quasi-homogeneous ignitions were achieved previously in non-resonant operation. To achieve a resonant operation, which goes along with a higher firing frequency, lower ignition and injection times are required. For this purpose, an array of solenoid valves was designed to allow for highly dynamic operation within short filling time spans. Using a novel mixed-integer control approach, these solenoid valves were actuated such that a desired fuel profile was generated. In this paper, the mentioned test rig was used for non-reacting fuel measurements to compare the quality of the axial fuel stratification achieved by using the valve array with the one achieved by using a slower proportional valve. In the experimental investigation the actuation with the valve array proved to adjust the required fuel stratification with the same quality as the actuation with the proportional valve, which was already successfully applied to the reactive set-up. Hence, the mixed-integer controlled valve array is considered a useful concept for upcoming resonant reactive SEC investigations.

Direct Numerical Simulation of Partial Fuel Stratification Assisted Lean Premixed Combustion for Assessment of Hybrid G-Equation/Well-Stirred Reactor Model

2021 ◽  
Author(s):  
Chao Xu ◽  
Muhsin Ameen ◽  
Pinaki Pal ◽  
Sibendu Som
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Initial Conditions ◽  
Operating Conditions ◽  
Premixed Combustion ◽  
Lean Premixed Combustion ◽  
Fuel Stratification ◽  
Stirred Reactor ◽  
Lean Premixed ◽  
Flame Structures

Abstract Partial fuel stratification (PFS) is a promising fuel injection strategy to stabilize lean premixed combustion in spark-ignition (SI) engines. PFS creates a locally stratified mixture by injecting a fraction of the fuel, just before spark timing, into the engine cylinder containing homogeneous lean fuel/air mixture. This locally stratified mixture, when ignited, results in complex flame structure and propagation modes similar to partially premixed flames, and allows for faster and more stable flame propagation than a homogeneous lean mixture. This study focuses on understanding the detailed flame structures associated with PFS-assisted lean premixed combustion. First, a two-dimensional direct numerical simulation (DNS) is performed using detailed fuel chemistry, experimental pressure trace, and realistic initial conditions mapped from a prior engine large-eddy simulation (LES), replicating practical lean SI operating conditions. DNS results suggest that conventional triple flame structures are prevalent during the initial stage of flame kernel growth. Both premixed and non-premixed combustion modes are present with the premixed mode contributing dominantly to the total heat release. Detailed analysis reveals the effects of flame stretch and fuel pyrolysis on the flame displacement speed. Based on the DNS findings, the accuracy of a hybrid G-equation/well-stirred reactor (WSR) combustion model is assessed for PFS-assisted lean operation in the LES context. The G-equation model qualitatively captures the premixed branches of the triple flame, while the WSR model predicts the non-premixed branch of the triple flame. Finally, potential needs for improvements to the hybrid G-equation/WSR modeling approach are discussed.

Fuel Stratification Influence on NOx Emission in a Premixed Axial Reacting Jet-in-Crossflow at High Pressure

2021 ◽  
Vol 143 (12) ◽  
Author(s):  
Bernhard Stiehl ◽  
Tommy Genova ◽  
Michelle Otero ◽  
Scott Martin ◽  
Kareem Ahmed
Keyword(s):  
Equivalence Ratio ◽  
Vortex Pair ◽  
No Production ◽  
Nox Formation ◽  
Local Flow ◽  
Detailed Chemistry ◽  
Jet In Crossflow ◽  
Global Emission ◽  
Fuel Stratification ◽  
Jet Trajectory

Abstract Three reacting jet-in-crossflow (JiC) methane/air flames were numerically investigated in a lean axially staged combustor at a pressure of five atmospheres. A detailed chemistry Star-CCM+ computational fluid dynamics (CFD) model was used with 53 species considered and the result of turbulence-governed finite-rate modeling was validated with in-house experimental data. An optically accessible test section features three side windows, allowing local flow and flame analysis with particle image velocimetry (PIV) and CH* chemiluminescence as well as pressure, temperature, and species exit measurements. The research objective was to predict and verify NOx formation of the premixed 12.7 mm axial jet. Three headend temperature levels were investigated along with three premixed jets at lean (φJet = 0.75), near-stoichiometric (φJet = 1.07), and rich (φJet = 1.78) axial fuel line equivalence ratio. Based on the matching exit emission concentration, global emission benefits were investigated by adjustment of the fuel stratification. The perfectly premixed methane/air flames of this study were shown to ignite at the lee-side of the jet. For the elevated headend temperature level T = 1800 K, the flame extended beyond the windward jet trajectory and caused high axial NO production. For industry application, a firing temperature of 1920 K was achieved with a NOx optimized fuel split of 25%, combining a lean headend (φHeadend = 0.61) with a rich (φJet = 1.78) jet equivalence ratio. This operating point allowed minimization of the combustor residence time at temperatures above 1700 K as well as combustion in a compact flame at the jet lee-side along the counter rotating vortex pair.

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