Alabama Transportation Institute

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Catalytic partial oxidation reformation of diesel, gasoline, and natural gas for use in low temperature combustion engines
(Elsevier, 2019) Hariharan, Deivanayagam; Yang, Ruinan; Zhou, Yingcong; Gainey, Brian; Mamalis, Sotirios; Smith, Robyn E.; Lugo-Pimentel, Michael A.; Castaldi, Marco J.; Gill, Rajinder; Davis, Andrew; Modroukas, Dean; Lawler, Benjamin; State University of New York (SUNY) System; State University of New York (SUNY) Stony Brook; City University of New York (CUNY) System; City College of New York (CUNY); University of Alabama Tuscaloosa
Onboard reforming has relevance to both conventional and advanced combustion concepts. Most recently, onboard reforming has been proposed to enable "Single-Fuel RCCI" combustion and therefore, this paper explores catalytic partial oxidation reforming of three potential transportation-relevant fuels: gasoline, diesel, and natural gas. Reformation is performed at two pressure levels (between 15 and 60 psig) for each parent fuel for equivalence ratios ranging from 3.7 to 7.6 and the gaseous reformate mixtures are characterized with gas chromatography. The percentage of diesel oxidized during reformation is similar across all of the equivalence ratios. However, the percentage of gasoline and natural gas oxidized during reformation decreased with increasing equivalence ratio. The energy released during the reformation process is also calculated and presented for each gaseous reformate fuel. The lower heating value of every reformate fuel is lower than 20% of their respective parent fuel, due to the high concentration of inert gases (mostly nitrogen) in the reformate fuel mixtures. Two reformed fuels for each parent fuel were then selected to study their autoignition characteristics using HCCI combustion on a Co-operative Fuel Research (CFR) engine. The equivalence ratio is maintained at 0.31 and the combustion phasing was held constant by varying the intake temperature. Although the equivalence ratio is constant, the input energy from the different reformate fuels is not constant due to the component concentrations in the fuel. The gaseous reformate fuels are then compared to gasoline, natural gas, and the primary reference fuels in HCCI to determine an effective Primary Reference Fuel (PRF) number or effective octane rating for each gaseous reformate fuel. The effective octane rating for the gaseous reformate fuels fell slightly above the PRF number scale at an effective octane number of -110.
Effects of Single versus Two-Stage Heat Release on the Load Limits of HCCI using Primary Reference Fuels
(2019) Hariharan, Deivanayagam; Yang, Ruinan; Mamalis, Sotirios; Lawler, Benjamin; University of Alabama Tuscaloosa
Homogeneous Charge Compression Ignition (HCCI) enables combustion with high efficiency and low emissions. Control over the combustion process and its narrow operating range are still the biggest challenges associated with HCCI. To expand the operable load ranges of HCCI, this paper explores the effects of single versus two-stage ignition fuels by studying the Primary Reference Fuels (PRF) in a variable compression ratio Cooperative Fuel Research (CFR) engine. The PRF fuels, iso-octane and n-heptane, are blended together at various concentrations to create fuel blends with different autoignition characteristics. Experiments were conducted using these PRF blends to explore the extent to which the load range can be extended with two-stage ignition fuels at various compression ratios and intake temperatures. The reactivity of the PRF blends increases with the fraction of n-heptane and so does the amount of low temperature heat release (LTHR). Since the low PRF number fuels have a higher reactivity, they can be autoignited at very low compression ratios while maintaining comparable combustion phasing and equivalence ratios. At the lower compression ratios, the low load limits were found to be extended while maintaining high combustion efficiencies. Additionally, lower peak pressures and pressure rise rates were achieved at low PRF number fuels as a result of its two-stage heat release, which can be used to reach higher loads. In addition, the energy released from the LTHR can be used to delay the CA50 combustion phasing (i.e., the crank angle timing where 50% of the energy has been released) beyond what is possible with a single-stage ignition fuel, which allows further high load extension. However, using lower compression ratios has a negative impact on the thermal efficiency. The effects of the extended load, single- and two-stage heat release, combustion phasing, and equivalence ratios on combustion efficiency, thermal efficiencies, and combustion durations were also explored.
Efficiency and Emissions Characteristics of an HCCl Engine Fueled by Primary Reference Fuels
(SAE International, 2018) Yang, Ruinan; Hariharan, Deivanayagam; Zilg, Steven; Mamalis, Sotirios; Lawler, Benjamin; State University of New York (SUNY) System; State University of New York (SUNY) Stony Brook; University of Alabama Tuscaloosa
This article investigates the effects of various primary reference fuel (PRF) blends, compression ratios, and intake temperatures on the thermodynamics and performance of homogeneous charge compression ignition (HCCl) combustion in a Cooperative Fuels Research (CFR) engine. Combustion phasing was kept constant at a CA50 phasing of 5 degrees after top dead center (aTDC) and the equivalence ratio was kept constant at 0.3. Meanwhile, the compression ratio varied from 8:1 to 15:1 as the PRF blends ranged from pure n-heptane to nearly pure isooctane. The intake temperature was used to match CA50 phasing. In addition to the experimental results, a GT-Power model was constructed to simulate the experimental engine and the model was validated against the experimental data. The GT-Power model and simulation results were used to help analyze the energy flows and thermodynamic conditions tested in the experiment. The results indicate that an increase of compression ratio causes higher thermal efficiency and fuel conversion efficiency; however, at the same compression ratio, an increase in PRF number results in lower efficiency due to the required increase in intake temperature and the associated decrease in charge density. While the efficiency does increase with compression ratio, the results show that the effect of increased expansion work is partially offset by higher heat transfer losses and lower ratios of specific heats at higher compression ratios. The results indicate that the maximum pressure rise rate (MPRR) in HCCl significantly increases with compression ratio. Combustion efficiency shows a strong trend with peak temperature regardless of the PRF number or compression ratio, indicating that the CO-to-CO2 conversion is independent of the parent fuel chemistry in the case of the PRFs, whereas the unburned hydrocarbon emissions showed the opposite trend, depending mostly on the parent fuel's autoignition tendency.
Experimental study of lean spark ignition combustion using gasoline, ethanol, natural gas, and syngas
(Elsevier, 2019) Ran, Zhongnan; Hariharan, Deivanayagam; Lawler, Benjamin; Mamalis, Sotirios; State University of New York (SUNY) System; State University of New York (SUNY) Stony Brook; University of Alabama Tuscaloosa
In the development of internal combustion engines, engineers and researchers are facing the challenge of improving engine efficiency while reducing harmful exhaust emissions. Previous research has shown that lean combustion is one of the viable techniques that can improve engine efficiency while effectively reducing exhaust emissions. Lean burn engines operate at low burned gas temperatures and can achieve high thermal efficiency based on favorable mixture thermodynamic properties. However, under high dilution levels, a lean misfire limit is reached where the combustion process becomes unstable and incomplete combustion starts to occur. Instability significantly affects engine efficiency, driveability, and exhaust emissions, which limit the full potential of lean burn engines. The lean misfire limit is not only dependent on engine design but also on fuel properties. Therefore, fuels that are conducive to lean combustion can provide the opportunity for enhanced efficiency and reduced emissions. Spark ignited (SI) combustion with conventional gasoline has shown to have relatively narrow range of fuel-air equivalence ratio; therefore, it is desired to explore the lean limit of SI combustion by using alternative fuels, which can also contribute to the reduction of greenhouse gas emissions from transportation and power generation. Experiments were conducted on a Cooperative Fuel Research (CFR) engine with varying fuel-air equivalence ratio (phi) to assess the engine performance and emissions with three alternative fuels, natural gas, ethanol, and syngas, at compression ratio of 8:1 and engine speed of 1200 rev/min. Equivalence ratio was varied by decreasing the mass of fuel while keeping the mass of air the same. The lean misfire limit was defined as the equivalence ratio where the CoV of IMEP across multiple consecutive engine cycles was greater than 5%. It was found that syngas can maintain stable combustion at extremely lean conditions and has the lowest lean misfire limit. Natural gas combustion achieved a lower lean misfire limit than gasoline and ethanol. Gasoline and ethanol had similar lean misfire limits, but it was found that gasoline helped the engine to achieve higher load and fuel conversion efficiency compared to the three alternative fuels.
Experimental Study of Spark-Ignition Combustion using the Anode Off-Gas from a Solid Oxide Fuel Cell
(2020) Ran, Zhongnan; Assanis, Dimitris; Hariharan, Deivanayagam; Mamalis, Sotirios; University of Alabama Tuscaloosa
Hybridizing Solid Oxide Fuel Cells (SOFCs) with internal combustion engines is an attractive solution for power generation at high electrical conversion efficiency while emitting significantly reduced emissions than conventional fossil fueled plants. The gas that exits the anode of an SOFC operating on natural gas is a mixture of H2, CO, CO2, and H2O vapor, which are the products of the fuel reforming and the electrochemical process in the stack. In this study, experiments were conducted on a single-cylinder, spark-ignited Cooperative Fuel Research Engine using the anode off-gas as the fuel, at compression ratio of 11:1 and 13:1, engine speed of 1200 rev/min and intake pressure of 75 kPa, to investigate the combustion characteristics and emissions formation. A comparison was drawn with combustion with Compressed Natural Gas (CNG) at the same engine operating conditions. The experimental results revealed that the anode off-gas can be used as a potential alternative fuel for spark-ignition combustion, and an engine can be used to provide additional power to a hybrid SOFC-engine system. Combustion with the anode off-gas resulted in similar net indicated efficiency with CNG at CR of 13:1, but with negligible NOx emissions and zero total hydrocarbon emissions. However, combustion with the anode off-gas resulted in lower volumetric efficiency and lower load than CNG as a result of high levels of dilution in the off-gas, which greatly reduces the lower heating value of the fuel. This study demonstrated the feasibility of using the SOFC anode-off gas as a potential fuel for spark-ignition engines with good fuel conversion efficiency and minimal NOx and THC emissions.
Experimental Study of the Effect of Start of Injection and Blend Ratio on Single Fuel Reformate RCCI
(ASME, 2020) Hariharan, Deivanayagam; Gainey, Brian; Yan, Ziming; Mamalis, Sotirios; Lawler, Benjamin; University of Alabama Tuscaloosa; Clemson University; State University of New York (SUNY) System; State University of New York (SUNY) Stony Brook
A new concept of single fuel reactivity-controlled compression ignition (RCCI) has been proposed through the catalytic partial oxidation (CPOX) reformation of diesel fuel. The reformed fuel mixture is then used as the low reactivity fuel and diesel itself is used as the high reactivity fuel. In this paper, two reformate mixtures from the reformation of diesel were selected for further analysis. Each reformate fuel mixture contained a significant fraction of inert gases (89% and 81%). The effects of the difference in the molar concentrations of the reformate mixtures were studied by experimenting with diesel as the direct injected fuel in RCCI over a varying start of injection timings and different blend ratios (i.e., the fraction of low and high reactivity fuels). The reformate mixture with the lower inert gas concentration had earlier combustion phasing and shorter combustion duration at any given diesel start of injection timing. The higher reactivity separation between reformate mixture and diesel, compared with gasoline and diesel, causes the combustion phasing of reformate-diesel RCCI to be more sensitive to the start of injection timing. The maximum combustion efficiency was found at a CA50 before top dead center (TDC), whereas the maximum thermal efficiency occurs at a CA50 after TDC. The range of energy-based blend ratios in which reformate-diesel RCCI is possible is between 25% and 45%, limited by ringing intensity (RI) at the low limit of blend ratios, and coefficient of variance (COV) of net indicated mean effective pressure (IMEPn) and combustion efficiency at the high limit. Intake boosting becomes necessary due to the oxygen deficiency caused by the low energy density of the reformate mixtures as it displaces intake air.
Single-fuel reactivity controlled compression ignition through catalytic partial oxidation reformation of diesel fuel
(Elsevier, 2019) Hariharan, Deivanayagam; Boldaji, Mozhgan Rahimi; Yan, Ziming; Mamalis, Sotirios; Lawler, Benjamin; State University of New York (SUNY) System; State University of New York (SUNY) Stony Brook; Clemson University; University of Alabama Tuscaloosa
A single-fuel RCCI concept has been proposed to avoid the need for a secondary fuel system required for conventional RCCI by generating the secondary fuel from the primary fuel through catalytic partial oxidation (CPOX) reformation. In conventional RCCI, gasoline or natural gas can be used as the low-reactivity fuel, and diesel can be used as the high-reactivity fuel. In this study, two reformate mixtures generated by reforming diesel fuel at different operating conditions were used as the low-reactivity fuel, with the parent diesel as the high reactivity fuel. The combustion characteristics of reformate-diesel RCCI were compared with the conventional RCCI. A CFD model was also developed and validated against the experimental results. The model was then used to validate a necessary approximation of the reformate mixture's species concentrations. Compared to conventional RCCI fuel pairs, reformate-diesel RCCI shows marginally better thermal efficiency, approximately 10% better THC emissions, approximately 50% lower NOx emissions, and good controllability. Because the reformate mixture has a high concentration of diluents it displaces a large fraction of intake air and acts similarly to EGR. The combustion behavior of reformate-diesel RCCI is in between that of gasoline-diesel and natural gas-diesel conventional RCCI. From the results, it can be concluded that reformate-diesel RCCI is not overly sensitive to the reformation process itself and the exact species concentrations in the reformate mixture. A small change in the start of injection of diesel, blend ratio, and EGR fraction can be used to compensate for reformate mixture concentration differences.

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Browsing Alabama Transportation Institute by Author "Mamalis, Sotirios"

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