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Compatibility of Elastomers with Oxymethylene Ethers and Blends with Diesel Fuel

Oak Ridge National Laboratory-Michael Kass, Martin Wissink, Chris Janke, Raynella Connatser, Scott Curran
  • Technical Paper
  • 2020-01-0620
To be published on 2020-04-14 by SAE International in United States
Oxymethylene ethers (OMEs) have shown promise as candidates for diesel fuel blendstocks due to their low sooting tendency, high cetane number, and diesel-comparable boiling point range. However, there is a lack of literature regarding compatibility of OMEs with common automotive elastomers, which would be a prerequisite to their adoption into the marketplace. To address this need, an exposure study and complementary solubility analysis were undertaken. A commercially available blend of OMEs with polymerization degree ranging from 3 to 6 was blended with diesel certification fuel at 0, 33, 67, at 100% by volume. Elastomer coupons were exposed to the various blends for a period of 4 weeks and evaluated for volume swell. The elastomer materials included multiple fluoroelastomers (Viton and fluorosilicone) and acrylonitrile butadiene rubbers (NBR), as well as neoprene, polyurethane, epichlorohydrin (ECO), PVC-nitrile blend (OZO), ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR), and silicone. The exposure results indicated overall poor compatibility for OME, with every elastomer except for fluorosilicone exhibiting greater than 30% volume swell at the 33% blend level. The general trend…
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Ignition Delay in Low Temperature Combustion

Missouri S&T-Joseph Drallmeier
Oak Ridge National Laboratory-Martin Wissink, Scott Curran, Robert Wagner
Published 2018-04-03 by SAE International in United States
Low temperature combustion (LTC) strategies present a means of reducing soot and oxides of nitrogen (NOx) emissions while simultaneously increasing efficiency relative to conventional combustion modes. By sufficiently premixing fuel and air before combustion, LTC strategies avoid high fuel-to-air equivalence ratios that lead to soot production. Dilution of the mixture lowers the combustion temperatures to reduce NOx production and offers thermodynamic advantages for improved efficiency. However, issues such as high heat release rates (HRRs), incomplete combustion, and difficulty in controlling the timing of combustion arise with low equivalence ratios and combustion temperatures. Ignition delay (the time until the start of combustion) is a way to quantify the time available for fuel and air to mix inside the cylinder before combustion. Previous studies have used ignition delay to explain trends seen in LTC such as combustion stability and HRRs. This study provides a novel method of integrating ignition delay into the investigation of LTC to determine what insights ignition delay calculations can provide for the different challenges associated with LTC strategies. To eliminate the need for…
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RCCI Combustion Regime Transitions in a Single-Cylinder Optical Engine and a Multi-Cylinder Metal Engine

SAE International Journal of Engines

Oak Ridge National Laboratory-Martin Wissink, Scott Curran
Sandia National Laboratories-Gregory Roberts, Mark Musculus
  • Journal Article
  • 2017-24-0088
Published 2017-09-04 by SAE International in United States
Reactivity Controlled Compression Ignition (RCCI) is an approach to increase engine efficiency and lower engine-out emissions by using in-cylinder stratification of fuels with differing reactivity (i.e., autoignition characteristics) to control combustion phasing. Stratification can be altered by varying the injection timing of the high-reactivity fuel, causing transitions across multiple regimes of combustion. When injection is sufficiently early, combustion approaches a highly-premixed autoignition regime, and when it is sufficiently late it approaches more mixing-controlled, diesel-like conditions. Engine performance, emissions, and control authority over combustion phasing with injection timing are most favorable in between, within the RCCI regime.To study charge preparation phenomena that dictate regime transitions, two different optical diagnostics are applied in a single-cylinder heavy-duty optical engine, and conventional engine diagnostics are applied in a multi-cylinder, light-duty all-metal engine. Both engines are operated with iso-octane and n-heptane as the low- and high-reactivity fuels, respectively. The iso-octane fuel fraction delivers 80% of the total fuel energy, the global equivalence ratio is 0.35, and no exhaust gas recirculation is used. In the optical engine, single-shot, band-pass infrared (IR)…
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Exploring the Role of Reactivity Gradients in Direct Dual Fuel Stratification

SAE International Journal of Engines

University of Wisconsin-Martin Wissink, Rolf Reitz
  • Journal Article
  • 2016-01-0774
Published 2016-04-05 by SAE International in United States
Low-temperature combustion (LTC) strategies have been an active area of research due to their ability to achieve high thermal efficiency while avoiding the formation of NOx and particulate matter. One of the largest challenges with LTC is the relative lack of authority over the heat release rate profile, which, depending on the particular injection strategy, either limits the maximum attainable load, or creates a tradeoff between noise and efficiency at high load conditions. We have shown previously that control over heat release can be dramatically improved through a combination of reactivity stratification in the premixed charge and a diffusion-limited injection that occurs after the conclusion of the low-temperature heat release, in a strategy called direct dual fuel stratification (DDFS). This paper will focus on the role the of the reactivity gradients in the premixed charge, which are achieved by the relatively early injection of gasoline and the relatively late injection of diesel. Three regimes were identified for the diesel injection timing: premixed, reactivity-controlled, and diffusion-limited, with the reactivity-controlled regime being observed to offer superior control…
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Direct Dual Fuel Stratification, a Path to Combine the Benefits of RCCI and PPC

SAE International Journal of Engines

University of Wisconsin-Martin Wissink, Rolf D. Reitz
  • Journal Article
  • 2015-01-0856
Published 2015-04-14 by SAE International in United States
Control of the timing and magnitude of heat release is one of the biggest challenges for premixed compression ignition, especially when attempting to operate at high load. Single-fuel strategies such as partially premixed combustion (PPC) use direct injection of gasoline to stratify equivalence ratio and retard heat release, thereby reducing pressure rise rate and enabling high load operation. However, retarding the heat release also reduces the maximum work extraction, effectively creating a tradeoff between efficiency and noise. Dual-fuel strategies such as reactivity controlled compression ignition (RCCI) use premixed gasoline and direct injection of diesel to stratify both equivalence ratio and fuel reactivity, which allows for greater control over the timing and duration of heat release. This enables combustion phasing closer to top dead center (TDC), which is thermodynamically favorable. However, the main control mechanism in RCCI is the ratio of the two fuels, and the diesel fraction typically reaches zero before full load is achieved. We propose a new strategy that effectively combines the benefits of RCCI and PPC by injecting both gasoline and diesel…
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Isobutanol as Both Low Reactivity and High Reactivity Fuels with Addition of Di-Tert Butyl Peroxide (DTBP) in RCCI Combustion

SAE International Journal of Fuels and Lubricants

University of Wisconsin-Dan DelVescovo, Hu Wang, Martin Wissink, Rolf D. Reitz
  • Journal Article
  • 2015-01-0839
Published 2015-04-14 by SAE International in United States
Engine experiments and multi-dimensional modeling were used to explore the effects of isobutanol as both the high and low reactivity fuels in Reactivity Controlled Compression Ignition (RCCI) Combustion. Three fuel combinations were examined; EEE/diesel, isobutanol/diesel, and isobutanol/isobutanol+DTBP (di-tert butyl peroxide). In order to assess the relative performance of the fuel combinations of interest under RCCI operation, the engine was operated under conditions representative of typical low temperature combustion (LTC). A net load of 6 bar indicated mean effective pressure (IMEP) was chosen because it provides a wide operable range of equivalence ratios and combustion phasings without excessively high peak pressure rise rates (PPRR). The engine was operated under various intake pressures with global equivalence ratios from 0.28-0.36, and various combustion phasings (defined by 50% mass fraction burned-CA50) from about 1.5 to about 10 deg after top dead center (ATDC). Combustion phasing was varied by scaling the direct-injected fuel quantity appropriately.Due to isobutanol's high octane number, a significantly larger quantity of direct-injected fuel was required to match combustion phasing, resulting in higher NOx emissions and decreased…
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Effects of Temporal and Spatial Distributions of Ignition and Combustion on Thermal Efficiency and Combustion Noise in DICI Engine

Tsinghua Univ.-Jian Huang, Zhi Wang
Univ. of Wisconsin-Martin Wissink, Rolf D. Reitz
Published 2014-04-01 by SAE International in United States
The effects of the temporal and spatial distributions of ignition timings of combustion zones on combustion noise in a Direct Injection Compression Ignition (DICI) engine were studied using experimental tests and numerical simulations. The experiments were performed with different fuel injection strategies on a heavy-duty diesel engine. Cylinder pressure was measured with the sampling intervals of 0.1°CA in order to resolve noise components. The simulations were performed using the KIVA-3V code with detailed chemistry to analyze the in-cylinder ignition and combustion processes. The experimental results show that optimal sequential ignition and spatial distribution of combustion zones can be realized by adopting a two-stage injection strategy in which the proportion of the pilot injection fuel and the timings of the injections can be used to control the combustion process, thus resulting in simultaneously higher thermal efficiency and lower noise emissions. Simulated results show that if a large amount of the combustion occurs near the liner walls of the combustion chamber, this significantly contributes to high amplitude pressure oscillations, which leads to heavy knock and low thermal…
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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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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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RCCI Engine Operation Towards 60% Thermal Efficiency

Univ of Wisconsin-Derek Splitter, Martin Wissink, Dan DelVescovo, Rolf D. Reitz
Published 2013-04-08 by SAE International in United States
The present experimental study explored methods to obtain the maximum practical cycle efficiency with Reactivity Controlled Compression Ignition (RCCI). The study used both zero-dimensional computational cycle simulations and engine experiments. The experiments were conducted using a single-cylinder heavy-duty research diesel engine adapted for dual fuel operation, with and without piston oil gallery cooling. In previous studies, RCCI combustion with in-cylinder fuel blending using port-fuel-injection of a low reactivity fuel and optimized direct-injections of higher reactivity fuels was demonstrated to permit near-zero levels of NOx and PM emissions in-cylinder, while simultaneously realizing gross indicated thermal efficiencies in excess of 56%.The present study considered RCCI operation at a fixed load condition of 6.5 bar IMEP an engine speed of 1,300 [r/min]. The experiments used a piston with a flat profile with 18.7:1 compression ratio. The results demonstrated that the indicated gross thermal efficiency could be increased by not cooling the piston, by using high dilution, and by optimizing in-cylinder fuel stratification with two fuels of large reactivity differences. The best results achieved gross indicated thermal efficiencies near…
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