Alabama Transportation Institute

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Browsing Alabama Transportation Institute by Subject "Combustion and combustion processes"

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    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.
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    The Effects of Thick Thermal Barrier Coatings on Low-Temperature Combustion
    (2020) Yan, Ziming; Gainey, Brian; Gohn, James; Hariharan, Deivanayagam; Saputo, John; Schmidt, Carl; Caliari, Felipe; Sampath, Sanjay; Lawler, Benjamin; University of Alabama Tuscaloosa
    An experimental study was conducted on a Ricardo Hydra single-cylinder light-duty diesel research engine. Start of Injection (SOI) timing sweeps from -350 deg aTDC to -210 deg aTDC were performed on a total number of five pistons including two baseline metal pistons and three coated pistons to investigate the effects of thick thermal barrier coatings (TBCs) on the efficiency and emissions of low-temperature combustion (LTC). A fuel with a high latent heat of vaporization, wet ethanol, was chosen to eliminate the undesired effects of thick TBCs on volumetric efficiency. Additionally, the higher surface temperatures of the TBCs can be used to help vaporize the high heat of vaporization fuel and avoid excessive wall wetting. A specialized injector with a 60° included angle was used to target the fuel spray at the surface of the coated piston. Throughout the experiments, the equivalence ratio, ϕ, was maintained constant at 0.4; the combustion phasing was consistently matched at 6.8 ± 0.4 deg aTDC. It can be concluded that the thick TBC cases achieved 1 to 2 percentage points improvement in combustion efficiency, and generally, a ~2 percentage points increase in indicated engine efficiency. It is also noticed that applying a dense top sealing layer to the TBC further improves the UHC emissions compared to the TBC coated piston with an unsealed surface. From the heat release analysis, it can be concluded that the TBCs have no significant impact on the heat release process and knock intensity while matching the combustion phasing; however, it reduces the intake temperature requirement by up to 20 K. The exhaust gas temperatures were expected to increase for the TBC cases, but the expected increase in exhaust temperature was not conclusive from the results observed in this study.
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    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.