Charge Motion Analysis to Guide Engine Port Development and Enhance Combustion Stability for High Cooled Exhaust Gas Recirculation

An experimental study was carried out to evaluate the potential of hydrogen enrichment to increase the tolerance of a stoichiometrically fuelled natural gas engine to high levels of dilution by exhaust gas recirculation (EGR). This provides significant gains in terms of exhaust emissions without the rapid reduction in combustion stability typically seen when applying EGR to a methane-fuelled engine. Presented results give the envelope of benefits from hydrogen enrichment. In parallel, the performance of a catalytic exhaust gas reforming reactor was investigated in order that it could be used as an onboard source of hydrogen-rich EGR. It was shown that sufficient hydrogen was generated with currently available prototype catalysts to allow the engine, at the operating points considered, to tolerate up to 25 per cent EGR, while maintaining a coefficient of variability of indicated mean effective pressure below 5 per cent. This level of EGR gives a reduction in NO emissions greater than 80 per cent in all test cases.

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Extending Lean and Exhaust Gas Recirculation-Dilute Operating Limits of a Modern Gasoline Direct-Injection Engine Using a Low-Energy Transient Plasma Ignition System

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4033470 ◽

2016 ◽

Vol 138 (11) ◽

Cited By ~ 20

Author(s):

James Sevik ◽

Thomas Wallner ◽

Michael Pamminger ◽

Riccardo Scarcelli ◽

Dan Singleton ◽

...

Keyword(s):

Direct Injection ◽

Exhaust Gas Recirculation ◽

Low Energy ◽

Gasoline Direct Injection ◽

Combustion Stability ◽

Exhaust Gas ◽

Ignition System ◽

Plasma Ignition ◽

Gas Recirculation ◽

Transient Plasma

The efficiency improvement and emissions reduction potential of lean and exhaust gas recirculation (EGR)-dilute operation of spark-ignition gasoline engines is well understood and documented. However, dilute operation is generally limited by deteriorating combustion stability with increasing inert gas levels. The combustion stability decreases due to reduced mixture flame speeds resulting in significantly increased combustion initiation periods and burn durations. A study was designed and executed to evaluate the potential to extend lean and EGR-dilute limits using a low-energy transient plasma ignition system. The low-energy transient plasma was generated by nanosecond pulses and its performance compared to a conventional transistorized coil ignition (TCI) system operated on an automotive, gasoline direct-injection (GDI) single-cylinder research engine. The experimental assessment was focused on steady-state experiments at the part load condition of 1500 rpm 5.6 bar indicated mean effective pressure (IMEP), where dilution tolerance is particularly critical to improving efficiency and emission performance. Experimental results suggest that the energy delivery process of the low-energy transient plasma ignition system significantly improves part load dilution tolerance by reducing the early flame development period. Statistical analysis of relevant combustion metrics was performed in order to further investigate the effects of the advanced ignition system on combustion stability. Results confirm that at select operating conditions EGR tolerance and lean limit could be improved by as much as 20% (from 22.7 to 27.1% EGR) and nearly 10% (from λ = 1.55 to 1.7) with the low-energy transient plasma ignition system.

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Combustion and Emission Enhancement of a Spark Ignition Two-Stroke Cycle Engine Utilizing Internal and External Exhaust Gas Recirculation Approach at Low-Load Operation

Energies ◽

10.3390/en12040609 ◽

2019 ◽

Vol 12 (4) ◽

pp. 609 ◽

Cited By ~ 2

Author(s):

Amin Mahmoudzadeh Andwari ◽

Apostolos Pesyridis ◽

Vahid Esfahanian ◽

Mohd Said

Keyword(s):

Weight Ratio ◽

Exhaust Gas Recirculation ◽

Exhaust Emissions ◽

Combustion Stability ◽

Average Charge ◽

Exhaust Gas ◽

Low Load ◽

Gas Recirculation ◽

Charge Temperature ◽

Stroke Cycle

Two-stroke cycle engines have always been prominent due to their distinctive advantage incorporating high power-to-weight ratio, however the drawbacks are poor combustion efficiency, fuel short-circuiting and excessive emission of uHC and CO. These problems are apparent at low-load and speed regions and are the major obstacle to their global acceptance. The deficiencies can be addressed by increasing the in-cylinder average charge temperature employing Exhaust Gas Recirculation (EGR). An experimental study is conducted to investigate the influence of utilizing EGR techniques, including Internal and External EGR, on combustion misfiring occurrence, combustion stability and exhaust emissions using a single cylinder two-stroke SI engine at idling, low and mid-load conditions. From the results, it is observed since the average in-cylinder charge temperature is increased, due to utilizing EGRs, engine’s low and mid-load irregular combustions (misfire) and exhaust emissions are remarkably supressed and almost all of misfire cycles eliminated depending on the percentage of EGRs. In terms of combustion stability, it is agreed in general the application of EGRs improves the cyclic variation of IMEP, Pmax and CA10 compared to conventional operation. However, applying Ex-EGR compared to In-EGR will deteriorate cyclic variability of IMEP and CA10.

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Capturing Cyclic Variability in Exhaust Gas Recirculation Dilute Spark-Ignition Combustion Using Multicycle RANS

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4033184 ◽

2016 ◽

Vol 138 (11) ◽

Cited By ~ 4

Author(s):

Riccardo Scarcelli ◽

James Sevik ◽

Thomas Wallner ◽

Keith Richards ◽

Eric Pomraning ◽

...

Keyword(s):

Internal Combustion Engines ◽

Initial Conditions ◽

Exhaust Gas Recirculation ◽

Spark Ignition ◽

Operating Conditions ◽

Combustion Stability ◽

Exhaust Gas ◽

Cyclic Variability ◽

Ignition Characteristics ◽

Gas Recirculation

Dilute combustion is an effective approach to increase the thermal efficiency of spark-ignition (SI) internal combustion engines (ICEs). However, high dilution levels typically result in large cycle-to-cycle variations (CCV) and poor combustion stability, therefore limiting the efficiency improvement. In order to extend the dilution tolerance of SI engines, advanced ignition systems are the subject of extensive research. When simulating the effect of the ignition characteristics on CCV, providing a numerical result matching the measured average in-cylinder pressure trace does not deliver useful information regarding combustion stability. Typically large eddy simulations (LES) are performed to simulate cyclic engine variations, since Reynolds-averaged Navier–Stokes (RANS) modeling is expected to deliver an ensemble-averaged result. In this paper, it is shown that, when using RANS, the cyclic perturbations coming from different initial conditions at each cycle are not damped out even after many simulated cycles. As a result, multicycle RANS results feature cyclic variability. This allows evaluating the effect of advanced ignition sources on combustion stability but requires validation against the entire cycle-resolved experimental dataset. A single-cylinder gasoline direct injection (GDI) research engine is simulated using RANS and the numerical results for 20 consecutive engine cycles are evaluated for several operating conditions, including stoichiometric as well as exhaust gas recirculation (EGR) dilute operation. The effect of the ignition characteristics on CCV is also evaluated. Results show not only that multicycle RANS simulations can capture cyclic variability and deliver similar trends as the experimental data but more importantly that RANS might be an effective, lower-cost alternative to LES for the evaluation of ignition strategies for combustion systems that operate close to the stability limit.

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