A fundamental investigation into the relationship between lubricant composition and fuel ignition quality
AuthorsKuti, Olawole Abiola
Yang, Seung Yeon
Roberts, William L.
Chung, Suk Ho
Sarathy, S. Mani
KAUST DepartmentChemical Engineering Program
Clean Combustion Research Center
Combustion and Laser Diagnostics Laboratory
Combustion and Pyrolysis Chemistry (CPC) Group
Mechanical Engineering Program
Physical Science and Engineering (PSE) Division
high-pressure combustion (HPC) Research Group
Permanent link to this recordhttp://hdl.handle.net/10754/594070
MetadataShow full item record
AbstractA fundamental experiment involving the use of an ignition quality tester (IQT) was carried out to elucidate the effects of lubricant oil composition which could lead to low speed pre-ignition (LSPI) processes in direct injection spark ignition (DISI) engines. Prior to the IQT tests, lubricant base oils were analyzed using ultra-high resolution mass spectrometry to reveal their molecular composition. High molecular-weight hydrocarbons such as nC<inf>16</inf>H<inf>34</inf>, nC<inf>17</inf>H<inf>36</inf>, and nC<inf>18</inf>H<inf>38</inf> were selected as surrogates of lubricant base oil constituents, and then mixed with iso-octane (iC<inf>8</inf>H<inf>18</inf>-gasoline surrogate) in proportions of 1 vol.% (iC<inf>8</inf>H<inf>18</inf> = 99 vol.%) and 10 vol.% (iC<inf>8</inf>H<inf>18</inf> = 90 vol.%) for the IQT experiments. In addition, lubricant base oils such as SN100 (Group I) and HC4 and HC6 (Group III) and a fully formulated lubricant (SAE 20W50) were mixed with iso-octane in the same proportions. The IQT results were conducted at an ambient pressure of 15 bar and a temperature range of 680-873 K. In the temperature range of 710-850 K, the addition of 10 vol.% base oils surrogates, base oils, and lubricating oil to the 90 vol.% iC<inf>8</inf>H<inf>18</inf> reduces the average total ignition delay time by up to 54% for all mixtures, while the addition of 1 vol.% to 99 vol.% iC<inf>8</inf>H<inf>18</inf> yielded a 7% reduction within the same temperature range. The shorter total ignition delay was attributed to the higher reactivity of the lubricant base oil constituents in the fuel mixtures. A correlation between reactivity of base oils and their molecular composition was tentatively established. These results suggest that the lubricants have the propensity of initiating LSPI in DISI engines. Furthermore, similar results for n-alkanes, lubricant base oils, and fully formulated commercial lubricants suggest that it is the hydrocarbon fraction that contributes primarily to enhanced reactivity, and not the inorganic or organometallic additives.
CitationKuti, O. A., Yang, S. Y., Hourani, N., Naser, N., Roberts, W. L., Chung, S. H., & Sarathy, S. M. (2015). A fundamental investigation into the relationship between lubricant composition and fuel ignition quality. Fuel, 160, 605–613. doi:10.1016/j.fuel.2015.08.026
Showing items related by title, author, creator and subject.
Mechanism Triggering Pre-Ignition Events and Ideas to Avoid and Suppress Pre-Ignition in Turbocharged Spark-Ignited EnginesSingh, Eshan (2019-10) [Dissertation]
Advisor: Dibble, Robert W.
Committee members: Roberts, William Lafayette; Sarathy, Mani; Patzek, Tadeusz; Turner, JamieTurbocharged spark-ignited engines may encounter stochastic events of premature ignition of the fuel-air mixture, termed as pre-ignition. Pre-ignition often leads to extremely high peak pressure and pressure oscillations, causing engine damage. A review of pre-ignition in historic times is done in this dissertation, and the similarities and differences compared to modern pre-ignition issue are brought forth. Experiments conducted with varying injection strategies yielded varying pre-ignition tendency. The pre-ignition tendency correlated with the charge cooling tendency and the mass of liquid fuel impinging on the cylinder liner and diluting the oil film. The diluted oil is trapped in the piston ring area and from time-to-time gets launched into the combustion chamber near top dead center. The fuel-oil mixture droplet may ignite the surrounding charge before the spark timing. Experiments conducted with varying exhaust back pressure showed dependence of pre-ignition tendency on in-cylinder temperature near top dead center, for cases when intake pressure is higher than exhaust pressures. For exhaust pressure higher than intake pressure, fuel wall impingement was critical to pre-ignition. This research also devised ion-current based sensors for pre-ignition detection. Initial experiments were done with DC-power based ion-current sensor, which detected a pre-ignition event when a flame brushed past the sensor. There was a need of faster-response sensor with high signal-to-noise ratio, that would allow pre-ignition detection at its inception stage, thereby giving enough time to trigger an evasive action. In this regard, an AC-powered ion-current sensor was devised and patented. Sudden fuel enrichment at the time of pre-ignition detection was investigated as an evasive method. Various strategies were investigated for their pre-ignition suppression tendency. Split injection, water injection, Octane-on-Demand, injecting different fluids in late compression stroke and dual fuel operation with gasoline and methane were found to be highly effective at suppressing pre-ignition completely. Use of ethanol in blends with different FACE gasolines is investigated to suggest fuel effects on pre-ignition. The strategies were successful at either reducing the mass of liquid fuel impinging the liner, reducing the in-cylinder temperature near top dead center or reducing the potential of residual gas content to trigger pre-ignition in the next cycle.
Relating the octane numbers of fuels to ignition delay times measured in an ignition quality tester (IQT)Naser, Nimal; Yang, Seung Yeon; Kalghatgi, Gautam; Chung, Suk Ho (Fuel, Elsevier BV, 2016-09-21) [Article]A methodology for estimating the octane index (OI), the research octane number (RON) and the motor octane number (MON) using ignition delay times from a constant volume combustion chamber with liquid fuel injection is proposed by adopting an ignition quality tester. A baseline data of ignition delay times were determined using an ignition quality tester at a charge pressure of 21.3 bar between 770 and 850 K and an equivalence ratio of 0.7 for various primary reference fuels (PRFs, mixtures of isooctane and n-heptane). Our methodology was developed using ignition delay times for toluene reference fuels (mixtures of toluene and n-heptane). A correlation between the OI and the ignition delay time at the initial charge temperature enabled the OI of non-PRFs to be predicted at specified temperatures. The methodology was validated using ignition delay times for toluene primary reference fuels (ternary mixtures of toluene, iso-octane, and n-heptane), fuels for advanced combustion engines (FACE) gasolines, and certification gasolines. Using this methodology, the RON, the MON, and the octane sensitivity were estimated in agreement with values obtained from standard test methods. A correlation between derived cetane number and RON is also provided. (C) 2016 Elsevier Ltd. All rights reserved.
Pre-ignition associated with low-temperature shock tube ignition measurementsJaved, Tamour; Es-sebbar, Et-touhami; Jaasim, Mohammed; Badra, J.; Im, Hong G.; Farooq, Aamir (Combustion Institute, 2015-01-01) [Conference Paper]Shock tubes are widely used for chemical kinetics studies due to their ability to instantaneously achieve nearly zero-dimensional high-temperature conditions behind reflected shock waves. In an attempt to study ignition chemistry at lower temperatures, however, there are additional challenges and non-idealities associated with using shock tube for long test time. One such non-ideality is the gradual linear pressure rise behind the reflected shock wave, commonly known as the "dP/dt problem", which is resolved by time-dependent volume profile in homogeneous calculations. Another non-ideality, which thus far has been overlooked, is the pre-ignition pressure rise or pre-ignition energy release. In the current work, measurements of ignition delay times of n-heptane and n-hexane under low-temperature (650-1250 K) and low-pressure (1.5 atm) conditions are reported, in which significant discrepancies in the ignition delay time measurements and predictions are noted. Such non-ideal behavior is attributed to pre-ignition localized ignition kernels, and the postulate is validated by high-fidelity simulations at experimental conditions by demonstrating the level of ignition advancement caused by localized ignition sources.