A comparative study of gasoline skeletal mechanisms under partial fuel stratification conditions using large eddy simulations

2021 ◽  
pp. 146808742110313
Author(s):  
Gaurav Guleria ◽  
Dario Lopez-Pintor ◽  
John E Dec ◽  
Dimitris Assanis
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Chemical Kinetic ◽  
Large Eddy Simulations ◽  
Low Temperature Combustion ◽  
Fuel Stratification ◽  
Large Eddy ◽  
Kinetic Mechanisms ◽  
Temperature Combustion ◽  
Research Grade

Partial fuel stratification (PFS) is a low temperature combustion strategy that can alleviate high heat release rates of traditional low temperature combustion strategies by introducing compositional stratification in the combustion chamber using a split fuel injection strategy. In this study, a three-dimensional computational fluid dynamics (CFD) model with large eddy simulations and reduced detailed chemistry was used to model partial fuel stratification at three different stratified conditions. The double direct injection strategy injects 80% of the total fuel mass at −300 CAD aTDC and the remaining 20% of the fuel mass is injected at three different timings of −160, −50, −35 CAD to create low, medium, and high levels of compositional stratification, respectively. The PFS simulations were validated using experiments performed at Sandia National Laboratories on a single-cylinder research engine that operates on RD5-87, a research-grade E10 gasoline. The objective of this study is to compare the performance of three different reduced chemical kinetic mechanisms, namely SKM1, SKM2, and SKM3, at the three compositional stratification levels and identify the most suitable mechanism to reproduce the experimental data. Zero-dimensional chemical kinetic simulations were also performed to further understand differences in performance of the three reduced chemical kinetic mechanisms to explain variations in CFD derived heat release profiles. The modeling results indicate that SKM3 is the most suitable mechanism for partial fuel stratification modeling of research-grade gasoline. The results also show that the autoignition event progresses from the richer to the leaner compositional regions in the combustion chamber. Notably, the leaner regions that have less mass per unit volume, can contribute disproportionately more toward heat release as there are more cells at leaner equivalence ratio ranges. Overall, this study illuminates the underlying compositional stratification phenomena that control the heat release process in PFS combustion.

The role of the diffusion-limited injection in direct dual fuel stratification

2016 ◽  
Vol 18 (4) ◽  
pp. 351-365 ◽  
Author(s):  
Martin Wissink ◽  
Rolf Reitz
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Thermal Efficiency ◽  
Soot Formation ◽  
Combustion Stability ◽  
Dual Fuel ◽  
Low Temperature Combustion ◽  
Fuel Stratification ◽  
Diffusion Limited ◽  
Temperature Combustion

Low-temperature combustion offers an attractive combination of high thermal efficiency and low NO x and soot formation at moderate engine load. However, the kinetically-controlled nature of low-temperature combustion yields little authority over the rate of heat release, resulting in a tradeoff between load, noise, and thermal efficiency. While several single-fuel strategies have achieved full-load operation through the use of equivalence ratio stratification, they uniformly require retarded combustion phasing to maintain reasonable noise levels, which comes at the expense of thermal efficiency and combustion stability. Previous work has shown that control over heat release can be greatly improved by combining reactivity stratification in the premixed charge with a diffusion-limited injection that occurs after low-temperature heat release, in a strategy called direct dual fuel stratification. While the previous work has shown how the heat release control offered by direct dual fuel stratification differs from other strategies and how it is enabled by the reactivity stratification created by using two fuels, this paper investigates the effects of the diffusion-limited injection. In particular, the influence of fuel selection and the pressure, timing, and duration of the diffusion-limited injection are examined. Diffusion-limited injection fuel type had a large impact on soot formation, but no appreciable effect on performance or other emissions. Increasing injection pressure was observed to decrease filter smoke number exponentially while improving combustion efficiency. The timing and duration of the diffusion-limited injection offered precise control over the heat release event, but the operating space was limited by a tradeoff between NO x and soot.

Understanding partial fuel stratification for low temperature gasoline combustion using large eddy simulations

2020 ◽  
pp. 146808742092104
Author(s):  
Priya Priyadarshini ◽  
Aimilios Sofianopoulos ◽  
Sotirios Mamalis ◽  
Benjamin Lawler ◽  
Dario Lopez-Pintor ◽  
...  
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Direct Injection ◽  
Large Eddy Simulations ◽  
Compression Ignition ◽  
Load Range ◽  
Injection Strategy ◽  
Compression Ignition Engines ◽  
Fuel Stratification ◽  
Large Eddy

The development of gasoline compression ignition engines operating in a low temperature combustion mode depends heavily on robust control of the heat release profile. Partial fuel stratification is an effective method for controlling the heat release by creating a stratified mixture prior to autoignition, which can be beneficial for operation across a wide load range. In this study, three-dimensional large eddy simulations were used to model a double direct injection strategy for which 80% of the fuel was injected during the intake stroke, and 20% of the fuel was injected at varying timing during the compression stroke. The simulations replicated a set of experiments performed at Sandia National Laboratories on a 1-L single-cylinder research engine using E10 gasoline (gasoline fuel containing 10% vol. ethanol). The objective of this study is to analyze the effects of the double direct injection strategy on the compositional and thermal stratification of the mixture, and understand the best use of this operating strategy. The modeling results indicated that by retarding the start of the second injection, the mixture stratification increases, which can be used to control the autoignition timing and the combustion phasing. Ignition and CA50 (crank angle of 50% mass fraction burned) are dictated by the mass concentration of the richest zones in the combustion chamber, as well as their location. The richer zones have the lowest temperatures before ignition primarily due to evaporative cooling from direct fuel injection. Overall, this study enhances the understanding of partial fuel stratification that can be used for controlling the heat release in gasoline compression ignition engines.

CFD Analysis of Diesel-Methane Dual Fuel Low Temperature Combustion at Low Load and High Methane Substitution

2018 ◽  
Author(s):  
Andrea Aniello ◽  
Lorenzo Bartolucci ◽  
Stefano Cordiner ◽  
Vincenzo Mulone ◽  
Sundar R. Krishnan ◽  
...  
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Diesel Fuel ◽  
Single Stage ◽  
Dual Fuel ◽  
Low Temperature Combustion ◽  
Two Stage ◽  
Low Load ◽  
Temperature Heat ◽  
Temperature Combustion

Over the last few decades, emissions regulations for internal combustion engines have become increasingly restrictive, pushing researchers around the world to exploit innovative propulsion solutions. Among them, the dual fuel low temperature combustion (LTC) strategy has proven capable of reducing fuel consumption and while meeting emissions regulations for oxides of nitrogen (NOx) and particulate matter (PM) without problematic aftertreatment systems. However, further investigations are still needed to reduce engine-out hydrocarbon (HC) and carbon monoxide (CO) emissions as well as to extend the operational range and to further improve the performance and efficiency of dual-fuel engines. In this scenario, the present study focuses on numerical simulation of fumigated methane-diesel dual fuel LTC in a single-cylinder research engine (SCRE) operating at low load and high methane percent energy substitution (PES). Results are validated against experimental cylinder pressure and apparent heat release rate (AHRR) data. A 3D full-cylinder RANS simulation is used to thoroughly understand the influence of the start of injection (SOI) of diesel fuel on the overall combustion behavior, clarifying the causes of AHRR transition from two-stage AHRR at late SOIs to single-stage AHRR at early SOIs, low temperature heat release (LTHR) behavior, as well as high HC production. The numerical campaign shows that it is crucial to reliably represent the interaction between the diesel spray and the in-cylinder charge to match both local and overall methane energy fraction, which in turn, ensures a proper representation of the whole combustion. To that aim, even a slight deviation (∼3%) of the trapped mass or of the thermodynamic conditions would compromise the numerical accuracy, highlighting the importance of properly capturing all the phenomena occurring during the engine cycle. The comparison between numerical and experimental AHRR curves shows the capability of the numerical framework proposed to correctly represent the dual-fuel combustion process, including low temperature heat release (LTHR) and the transition from two-stage to single stage AHRR with advancing SOI. The numerical simulations allow for quantitative evaluation of the residence time of vapor-phase diesel fuel inside the combustion chamber and at the same time tracking the evolution of local diesel mass fraction during ignition delay — showing their influence on the LTHR phenomena. Oxidation regions of diesel and ignition points of methane are also displayed for each case, clarifying the reasons for the observed differences in combustion evolution at different SOIs.

Operating Limits of Spark-Assisted Compression Ignition Combustion Under Boosted Ultra-EGR Dilute Conditions in a Negative Valve Overlap Engine

2019 ◽  
Author(s):  
Vassilis Triantopoulos ◽  
Jason B. Martz ◽  
Jeff Sterniak ◽  
George Lavoie ◽  
Dennis N. Assanis ◽  
...  
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Engine Speed ◽  
Pressure Rise ◽  
Stability Limit ◽  
Maximum Pressure ◽  
Low Temperature Combustion ◽  
Compression Ignition ◽  
Temperature Combustion ◽  
Operating Limits

Abstract Spark-assisted compression ignition (SACI) is a low temperature combustion mode that can offer thermal efficiency improvements and lower nitrogen oxide emissions compared to conventional spark-ignited combustion. However, the SACI operating range is often limited due to excessive pressure rise rates driven by rapid heat release rates. Well-controlled experiments were performed to investigate the SACI operating limits under previously unexplored boosted, stoichiometric, EGR dilute conditions, where low temperature combustion engines promise high thermodynamic efficiencies. At higher intake boost, the SACI high load limit shifted towards lower fuel-to-charge equivalence ratio mixtures, creating a larger gap between the conventional spark-ignition EGR dilution limit and the boosted SACI operating limits. Combustion phasing retard was very effective at reducing maximum pressure rise rate levels until the stability limit, primarily due to slower end-gas burn rates. Gross fuel conversion efficiency improvements up to 10% were observed by using intake boost for either load expansion or dilution extension. Changes in engine speed necessitated changes in unburned gas temperature to match autoignition timing, but were shown to have negligible impact on the heat release profile on a crank angle basis. Lower engine speeds were favorable for load expansion, as time-based peak pressure rise rates scaled with engine speed.

Investigation of Low Temperature Combustion Regimes of Biodiesel With n-Butanol Injected in the Intake Manifold of a Compression Ignition Engine

2012 ◽  
Author(s):  
Valentin Soloiu ◽  
Marvin Duggan ◽  
Henry Ochieng ◽  
David Williams ◽  
Gustavo Molina ◽  
...  
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Combustion Chamber ◽  
Nox Reduction ◽  
Intake Manifold ◽  
Power Stroke ◽  
Low Temperature Combustion ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Temperature Combustion

In this study, the in-cylinder soot and NOx trade off was investigated in a Compression Engine by implementing Premixed Charge Compression Ignition (PCCI) coupled with Low Temperature Combustion (LTC) for selected regimes of 1–3 bars IMEP. In order to achieve that, an omnivorous (multi-fuel) single cylinder diesel engine was developed by injecting n-butanol in the intake port while being fueled with biodiesel by direct injection in the combustion chamber. By applying this methodology, the in-cylinder pressure decreased by 25% and peak pressure was delayed in the power stroke by about 8 CAD for the cycles in which the n-butanol was injected in the intake manifold at the engine speed of 800 rpm and low engine loads, corresponding to 1–3 bars IMEP. Compared with the baseline taken with ultra-low sulfur diesel no. 2 (USLD#2), the heat release presented a more complex shape. At 1–2 bars IMEP, the premixed charge stage of the combustion totally disappeared and a prolonged diffusion stage was found instead. At 3 bars IMEP, an early low temperature heat release was present that started 6 degrees (1.25 ms) earlier than the diesel reference heat release with a peak at 350 CAD corresponding to 1200 K. Heat losses from radiation of burned gas in the combustion chamber decreased by 10–50% while the soot emissions showed a significant decrease of about 98%, concomitantly with a 98% NOx reduction at 1 IMEP, and 77% at 3 IMEP, by controlling the combustion phases. Gaseous emissions were measured using an AVL SESAM FTIR and showed that there were high increases in CO, HC and NMHC emissions as a result of PCCI/LTC strategy; nevertheless, the technology is still under development. The results of this work indicate that n-butanol can be a very promising fuel alternative including for LTC regimes.

Low-Temperature Combustion Within a HSDI Diesel Engine Using Multiple-Injection Strategies

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Tiegang Fang ◽  
Robert E. Coverdill ◽  
Chia-Fon F. Lee ◽  
Robert A. White
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Injection Pressure ◽  
Diffusion Combustion ◽  
Injection Timing ◽  
Low Temperature Combustion ◽  
Conventional Combustion ◽  
Main Injection ◽  
Temperature Combustion ◽  
Injection Strategies

Low-temperature compression ignition combustion employing multiple-injection strategies in an optical high-speed direct injection diesel engine was investigated. Heat release characteristics were analyzed. The whole cycle combustion process was visualized by imaging the natural flame luminosity. The NOx emissions were measured in the exhaust pipe. The effects of the pilot injection timing, pilot fuel quantity, main injection timing, operating load, and injection pressure on the combustion and emissions were studied. Low-temperature combustion modes were achieved by using a small pilot injection with an injection timing much earlier than top dead center (TDC) followed by a main injection after TDC. The results were compared with conventional diesel (diffusion) combustion for comparison purposes. A premixed-combustion-dominated heat release rate pattern was seen for all the low-temperature combustion cases, while a typical diffusion flame combustion heat release rate was obtained for the conventional combustion case. A highly luminous flame was observed for the conventional combustion condition while a much less luminous flame was seen for the low-temperature combustion cases. For the higher-load and lower injection pressure cases, liquid fuel being injected into low-temperature premixed flame was observed for certain cases. Compared with the conventional diffusion combustion, simultaneous reductions in soot and NOx were obtained for the low-temperature combustion mode under similar operating loads. For high-load conditions, higher NOx emissions were obtained due to higher in-cylinder temperatures. However, compared with the conventional combustion case, a significant reduction in soot was achieved for the high-load conditions, which shows that increasing injection pressure greatly reduces soot emissions.

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