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Fuel-Lubricant Interactions on the Propensity for Stochastic Pre-Ignition

Driven Racing Oil-Lake Speed
National Renewable Energy Laboratory-Bradley Zigler, Jon Luecke
Published 2019-09-09 by SAE International in United States
This work explores the impact of the interaction of lubricant and fuel properties on the propensity for stochastic pre-ignition (SPI). Findings are based on statistically significant changes in SPI tendency and magnitude, as determined by measurements of cylinder pressure. Specifically, lubricant detergents, lubricant volatility, fuel volatility, fuel chemical composition, fuel-wall impingement, and engine load were varied to study the physical and chemical effects of fuel-lubricant interactions on SPI tendency. The work illustrates that at low loads, with fuels susceptible to SPI events, lubricant detergent package effects on SPI were non-significant. However, with changes to fuel distillation, fuel-wall impingement, and most importantly engine load, lubricant detergent effects could be observed even at reduced loads This suggests that there is a thermal effect associated with the higher load operation. It was hypothesized that the thermal effect was associated with lube oil nitrogenation. To test this theory, nitromethane (CH3NO2) was blended at 6.5% by volume CH3NO2 resulted in significant sensitivity to lubricant additive package effect on SPI, even at reduced loads where no lubricant sensitivity was observed without…
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The Reduced Effectiveness of EGR to Mitigate Knock at High Loads in Boosted SI Engines

SAE International Journal of Engines

Lawrence Livermore National Lab-Scott W. Wagnon, William J. Pitz, Marco Mehl
Oak Ridge National Laboratory-James P. Szybist, Derek Splitter
  • Journal Article
  • 2017-24-0061
Published 2017-09-04 by SAE International in United States
Numerous studies have demonstrated that exhaust gas recirculation (EGR) can attenuate knock propensity in spark ignition (SI) engines at naturally aspirated or lightly boosted conditions [1]. In this study, we investigate the role of cooled EGR under higher load conditions with multiple fuel compositions, where highly retarded combustion phasing typical of modern SI engines was used. It was found that under these conditions, EGR attenuation of knock is greatly reduced, where EGR doesn’t allow significant combustion phasing advance as it does under lighter load conditions. Detailed combustion analysis shows that when EGR is added, the polytropic coefficient increases causing the compressive pressure and temperature to increase. At sufficiently highly boosted conditions, the increase in polytropic coefficient and additional trapped mass from EGR can sufficiently reduce fuel ignition delay to overcome knock attenuation effects. Kinetic modeling demonstrates that the effectiveness of EGR to mitigate knock is highly dependent on the pressure-temperature condition. Experiments at 2000 rpm have confirmed reduced fuel ignition delay under highly boosted conditions relevant to modern downsized boosted SI engines, where in-cylinder pressure…
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Engine Operating Conditions and Fuel Properties on Pre-Spark Heat Release and SPI Promotion in SI Engines

SAE International Journal of Engines

Oak Ridge National Laboratory-Derek Splitter, Brian Kaul, James Szybist, Gurneesh Jatana
  • Journal Article
  • 2017-01-0688
Published 2017-03-28 by SAE International in United States
This work explores the dependence of fuel ignition delay on stochastic pre-ignition (SPI). Findings are based on bulk gas thermodynamic state, where the effects of kinetically controlled bulk gas pre-spark heat release (PSHR) are correlated to SPI tendency and magnitude. Specifically, residual gas and low temperature PSHR chemistry effects and observations are explored, which are found to be indicative of bulk gas conditions required for strong SPI events. Analyzed events range from non-knocking SPI to knocking SPI and even detonation SPI events in excess of 325 bar peak cylinder pressure. The work illustrates that singular SPI event count and magnitude are found to be proportional to PSHR of the bulk gas mixture and residual gas fraction. Cycle-to-cycle variability in trapped residual mass and temperature are found to impose variability in singular SPI event count and magnitude. However, clusters and short lived bursts of multiple SPI events are found to better correlate with fuel-wall interaction. The results highlight the interplay of bulk gas thermodynamics and SPI ignition source, on SPI event magnitude and cluster tendency. Moreover,…
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Effects of Fuel Composition on EGR Dilution Tolerance in Spark Ignited Engines

SAE International Journal of Engines

Oak Ridge National Laboratory-James P. Szybist, Derek Splitter
  • Journal Article
  • 2016-01-0715
Published 2016-04-05 by SAE International in United States
Fuel-specific differences in exhaust gas recirculation (EGR) dilution tolerance are studied in a modern, direct-injection single-cylinder research engine. A total of 6 model fuel blends are examined at a constant research octane number (RON) of 95 using n-heptane, isooctane, toluene, and ethanol. Laminar flame speeds for these mixtures, which are calculated using two different methods (an energy fraction mixing rule and a detailed kinetic simulation), span a range of about 6 cm/s. A nominal load of 350 kPa IMEPg at 2000 rpm is maintained with constant fueling and varying CA50 from 8-20 CAD aTDCf. EGR is increased until a COV of IMEP of 5% is reached. The results illustrate that flame speed affects EGR dilution tolerance; fuels with increased flame speeds have increased EGR tolerance. Specifically, flame speed correlates most closely to the initial flame kernel growth, measured as the time of ignition to 5% mass fraction burned. The effect of the latent heat of vaporization (HoV) on the flame speed is taken into account for the ethanol-containing fuels. At a 30 vol% blend level,…
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SI Engine Trends: A Historical Analysis with Future Projections

Oak Ridge National Laboratory-Derek Splitter
Univ. of Tennessee-Alexander Pawlowski
Published 2015-04-14 by SAE International in United States
It is well known that spark ignited engine performance and efficiency is closely coupled to fuel octane number. The present work combines historical and recent trends in spark ignition engines to build a database of engine design, performance, and fuel octane requirements over the past 80 years. The database consists of engine compression ratio, required fuel octane number, peak mean effective pressure, specific output, and combined unadjusted fuel economy for passenger vehicles and light trucks. Recent trends in engine performance, efficiency, and fuel octane number requirement were used to develop correlations of fuel octane number utilization, performance, specific output. The results show that historically, engine compression ratio and specific output have been strongly coupled to fuel octane number. However, over the last 15 years the sales weighted averages of compression ratios, specific output, and fuel economy have increased, while the market fuel octane has remained unchanged. Using the developed correlations, 10-year-out projections of engine performance, design, and fuel economy are estimated for various fuel octane numbers, both with and without turbocharging. The 10-year-out projection suggest…
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Direct Measurement and Chemical Speciation of Top Ring Zone Liquid During Engine Operation

Oak Ridge National Laboratory-Derek Splitter, Sam Lewis
University of Alabama-Barry Burrows
Published 2015-04-14 by SAE International in United States
The present manuscript consists of proof of concept experiments involving direct measurements and detailed chemical speciation from the top ring zone of a running engine. The work uses a naturally aspirated single cylinder utility engine that has been modified to allow direct liquid sample acquisition from behind the top ring. Samples were analyzed and speciated using gas chromatographic techniques. Results show that the liquid mixture in the top ring zone is neither neat lubricant nor fuel but a combination of the two with unique chemical properties. At the tested steady state no-load operating condition, the chemical species of the top ring zone liquid were found to be highly dependent on boiling point, where both low reactivity higher boiling point fuel species and lubricant are observed to be the dominant constituents. The results show that at least for the tested condition, approximately 25% of the top ring zone is comprised of gasoline fuel like molecules, which are dominated by high octane number aromatic species, while the remainder of the liquid is comprised of lubricant like species.
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Negative Valve Overlap Reforming Chemistry in Low-Oxygen Environments

SAE International Journal of Engines

Oak Ridge National Lab.-James P. Szybist, Derek Splitter, Vickey B. Kalaskar, Josh Pihl, Charles Daw
Sandia National Labs.-Richard R. Steeper
  • Journal Article
  • 2014-01-1188
Published 2014-04-01 by SAE International in United States
Fuel injection into the negative valve overlap (NVO) period is a common method for controlling combustion phasing in homogeneous charge compression ignition (HCCI) and other forms of advanced combustion. When fuel is injected into O2-deficient NVO conditions, a portion of the fuel can be converted to products containing significant levels of H2 and CO. Additionally, other short chain hydrocarbons are produced by means of thermal cracking, water-gas shift, and partial oxidation reactions. The present study experimentally investigates the fuel reforming chemistry that occurs during NVO. To this end, two very different experimental facilities are utilized and their results are compared. One facility is located at Oak Ridge National Laboratory, which uses a custom research engine cycle developed to isolate the NVO event from main combustion, allowing a steady stream of NVO reformate to be exhausted from the engine and chemically analyzed. The other experimental facility, located at Sandia National Laboratories, uses a dump valve to capture the exhaust from a single NVO event for analysis. Results from the two experiments are in excellent trend-wise agreement…
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Improving the Understanding of Intake and Charge Effects for Increasing RCCI Engine Efficiency

SAE International Journal of Engines

University of Wisconsin-Derek Splitter, Martin Wissink, Dan DelVescovo, Rolf D. Reitz
  • Journal Article
  • 2014-01-1325
Published 2014-04-01 by SAE International in United States
The present experimental engine efficiency study explores the effects of intake pressure and temperature, and premixed and global equivalence ratios on gross thermal efficiency (GTE) using the reactivity controlled compression ignition (RCCI) combustion strategy. Experiments were conducted in a heavy-duty single-cylinder engine at constant net load (IMEPn) of 8.45 bar, 1300 rev/min engine speed, with 0% EGR, and a 50% mass fraction burned combustion phasing (CA50) of 0.5°CA ATDC. The engine was port fueled with E85 for the low reactivity fuel and direct injected with 3.5% 2-ethylhexyl nitrate (EHN) doped into 91 anti-knock index (AKI) gasoline for the high-reactivity fuel. The resulting reactivity of the enhanced fuel corresponds to an AKI of approximately 56 and a cetane number of approximately 28.The engine was operated with a wide range of intake pressures and temperatures, and the ratio of low- to high-reactivity fuel was adjusted to maintain a fixed speed-phasing-load condition. This allowed for the investigation of several combinations of intake temperature, intake pressure, and charge stratification at otherwise constant thermodynamic conditions. The results show that sources…
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Intermediate Alcohol-Gasoline Blends, Fuels for Enabling Increased Engine Efficiency and Powertrain Possibilities

SAE International Journal of Fuels and Lubricants

Oak Ridge National Lab.-Derek Splitter, James Szybist
  • Journal Article
  • 2014-01-1231
Published 2014-04-01 by SAE International in United States
The present study experimentally investigates spark-ignited combustion with 87 AKI E0 gasoline in its neat form and in mid-level alcohol-gasoline blends with 24% vol./vol. iso-butanol-gasoline (IB24) and 30% vol./vol. ethanol-gasoline (E30). A single-cylinder research engine is used with a low and high compression ratio of 9.2:1 and 11.85:1 respectively. The engine is equipped with hydraulically actuated valves, laboratory intake air, and is capable of external exhaust gas recirculation (EGR). All fuels are operated to full-load conditions with λ=1, using both 0% and 15% external cooled EGR. The results demonstrate that higher octane number bio-fuels better utilize higher compression ratios with high stoichiometric torque capability. Specifically, the unique properties of ethanol enabled a doubling of the stoichiometric torque capability with the 11.85:1 compression ratio using E30 as compared to 87 AKI, up to 20 bar IMEPg at λ=1 (with 15% EGR, 18.5 bar with 0% EGR). EGR was shown to provide thermodynamic advantages with all fuels. The results demonstrate that E30 may further the downsizing and downspeeding of engines by achieving increased low speed torque, even…
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Investigation of Pressure Oscillation Modes and Audible Noise in RCCI, HCCI, and CDC

Tsinghua Univ-Zhi Wang
Univ of Wisconsin-Martin Wissink, Derek Splitter, Arsham Shahlari, Rolf D. Reitz
Published 2013-04-08 by SAE International in United States
This study uses Fourier analysis to investigate the relationship between the heat release event and the frequency composition of pressure oscillations in a variety of combustion modes. While kinetically-controlled combustion strategies such as HCCI and RCCI offer advantages over CDC in terms of efficiency and NOX emissions, their operational range is limited by audible knock and the possibility of engine damage stemming from high pressure rise rates and oscillations. Several criteria such as peak pressure rise rate, ringing intensity, and various knock indices have been developed to quantify these effects, but they fail to capture all of the dynamics required to form direct comparisons between different engines or combustion strategies. Experiments were performed with RCCI, HCCI, and CDC on a 2.44 L heavy-duty engine at 1300 RPM, generating a significant diversity of heat release profiles. Fourier and statistical analyses were used to examine the effect of both the average heat release as well as cyclic variations on the frequency and amplitude of pressure oscillations, and these were compared to existing knocking criteria. The results indicate…
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