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Experimental evaluation of a custom gasoline-like blend designed to simultaneously improve φ-sensitivity, RON and octane sensitivity.

Sandia National Laboratories-Dario Lopez Pintor, John Dec, Gerald Gentz
  • Technical Paper
  • 2020-01-1136
To be published on 2020-04-14 by SAE International in United States
φ-sensitivity is a fuel characteristic that has important benefits for the operation and control of low-temperature gasoline combustion (LTGC) engines. However, regular gasoline is only weakly φ–sensitive at naturally aspirated conditions, so intake boosting is required to take advantage of this property. Thus, there is strong motivation for designing gasoline-like blends that improve φ–sensitivity and simultaneously increase RON and octane sensitivity, to improve performance for LTGC and modern SI engines. In a previous study [SAE 2019-01-0961], a 5-component regulation-compliant fuel blend (CB#1) was computationally designed; and simulations showed promising results compared to regular E10 gasoline (RD5-87). The current study experimentally evaluates CB#1 in a LTGC research engine, and the results are compared to RD5-87. For premixed naturally aspirated conditions, the intake heating required to autoignite CB#1 was similar to RD5-87, ensuring that CB#1 can operate under these conditions as easily as regular gasoline. Furthermore, similar maximum engine loads were reached with both CB#1 and RD5-87 under premixed, high-boost conditions. An independent analysis showed that the RON and octane sensitivity were increased 1.3 and 3.6 units,…
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Combustion-Timing Control of Low-Temperature Gasoline Combustion (LTGC) Engines by Using Double Direct-Injections to Control Kinetic Rates

General Motors LLC-Jeremie Dernotte
Sandia National Laboratories-Gerald Gentz, Chunsheng Ji, Dario Lopez Pintor, John Dec
Published 2019-04-02 by SAE International in United States
Low-temperature gasoline combustion (LTGC) engines can provide high efficiencies and extremely low NOx and particulate emissions, but controlling the combustion timing remains a challenge. This paper explores the potential of Partial Fuel Stratification (PFS) to provide fast control of CA50 in an LTGC engine. Two different compression ratios are used (CR=16:1 and 14:1) that provide high efficiencies and are compatible with mixed-mode SI-LTGC engines. The fuel used is a research grade E10 gasoline (RON 92, MON 85) representative of a regular-grade market gasoline found in the United States. The fuel was supplied with a gasoline-type direct injector (GDI) mounted centrally in the cylinder. To create the PFS, the GDI injector was pulsed twice each engine cycle. First, an injection early in the intake stroke delivered the majority of the fuel (70 - 80%), establishing the minimum equivalence ratio in the charge. Then, a second injection supplied the remainder of the fuel (20 - 30%) at a variable timing during the compression stroke, from 200° to 330°CA (0°CA = TDC-intake, 360°CA = TDC-compression) to provide controlled…
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Φ-Sensitivity for LTGC Engines: Understanding the Fundamentals and Tailoring Fuel Blends to Maximize This Property

Sandia National Laboratories-Dario Lopez Pintor, John Dec, Gerald Gentz
Published 2019-04-02 by SAE International in United States
Φ-sensitivity is a fuel characteristic that has important benefits for the operation and control of low-temperature gasoline combustion (LTGC) engines. A fuel is φ-sensitive if its autoignition reactivity varies with the fuel/air equivalence ratio (φ). Thus, multiple-injection strategies can be used to create a φ-distribution that leads to several benefits. First, the φ-distribution causes a sequential autoignition that reduces the maximum heat release rate. This allows higher loads without knock and/or advanced combustion timing for higher efficiencies. Second, combustion phasing can be controlled by adjusting the fuel-injection strategy. Finally, experiments show that intermediate-temperature heat release (ITHR) increases with φ-sensitivity, increasing the allowable combustion retard and improving stability.A detailed mechanism was applied using CHEMKIN to understand the chemistry responsible for φ-sensitivity. For fuels with NTC behavior, φ-sensitivity is greatest in the NTC region due to enhanced ITHR reactions, which explains the experimental correlation between φ-sensitivity and ITHR. Under engine conditions, higher intake pressure means lower intake temperature to balance the reactivity, and both effects increase the φ-sensitivity. However, φ-sensitivity remains almost constant if decreased oxygen concentration…
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Refining Measurement Uncertainties in HCCI/LTGC Engine Experiments

Lawrence Livermore National Laboratory-Guillaume Petitpas, Russell Whitesides
Sandia National Laboratories-Jeremie Dernotte, John Dec
Published 2018-04-03 by SAE International in United States
This study presents estimates for measurement uncertainties for a Homogenous Charge Compression Ignition (HCCI)/Low-Temperature Gasoline Combustion (LTGC) engine testing facility. A previously presented framework for quantifying those uncertainties developed uncertainty estimates based on the transducers manufacturers’ published tolerances. The present work utilizes the framework with improved uncertainty estimates in order to more accurately represent the actual uncertainties of the data acquired in the HCCI/LTGC laboratory, which ultimately results in a reduction in the uncertainty from 30 to less than 1 kPa during the intake and exhaust strokes. Details of laboratory calibration techniques and commissioning runs are used to constrain the sensitivities of the transducers relative to manufacturer supplied values. The uncertainty framework is also extended to consider additional sources of uncertainty, including non-ideal engine volume history due to kinematic effects on the effective connecting rod length. Finally, the uncertainty propagation chain is analyzed to determine primary uncertainty sources, and mitigations are discussed.
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Spark Assist for CA50 Control and Improved Robustness in a Premixed LTGC Engine – Effects of Equivalence Ratio and Intake Boost

General Motors LLC-Jeremie Dernotte
Sandia National Laboratories-Gerald Gentz, John Dec
Published 2018-04-03 by SAE International in United States
Low-temperature gasoline combustion (LTGC) engines can deliver high efficiencies, with ultra-low emissions of nitrogen oxides (NOx) and particulate matter (PM). However, controlling the combustion timing and maintaining robust operation remains a challenge for LTGC engines. One promising technique to overcoming these challenges is spark assist (SA). In this work, well-controlled, fully premixed experiments are performed in a single-cylinder LTGC research engine at 1200 rpm using a cylinder head modified to accommodate a spark plug. Compression ratios (CR) of 16:1 and 14:1 were used during the experiments. Two different fuels were also tested, with properties representative of premium- and regular-grade market gasolines. SA was found to work well for both CRs and fuels. The equivalence ratio (ϕ) limits and the effect of intake-pressure boost on the ability of SA to compensate for a reduced Tin were studied. For the conditions studied, ϕ=0.42 was found to be most effective for SA. At lower equivalence ratios the flame propagation was too weak, whereas ϕ=0.45 was closer to the CI knock/stability limit, which resulted in a smaller range of CA50…
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Efficiency Improvement of Boosted Low-Temperature Gasoline Combustion Engines (LTGC) Using a Double Direct-Injection Strategy

Sandia National Laboratories-Jeremie Dernotte, John Dec, Chunsheng Ji
Published 2017-03-28 by SAE International in United States
For lean or dilute, boosted gasoline compression-ignition engines operating in a low-temperature combustion mode, creating a partially stratified fuel charge mixture prior to auto-ignition can be beneficial for reducing the heat-release rate (HRR) and the corresponding maximum rate of pressure rise. As a result, partial fuel stratification (PFS) can be used to increase load and/or efficiency without knock (i.e. without excessive ringing). In this work, a double direct-injection (D-DI) strategy is investigated for which the majority of the fuel is injected early in the intake stroke to create a relatively well-mixed background mixture, and the remaining fuel is injected in the latter part of the compression stroke to produce greater fuel stratification prior auto-ignition. Experiments were performed in a 1-liter single-cylinder engine modified for low-temperature gasoline combustion (LTGC) research. The main objective of this study is to quantify the effects on the HRR and efficiency gains possible by applying this D-DI fueling technique to a near-perfectly homogeneous mixture and to a moderately stratified mixture (all the fuel injected early in the intake stroke). For the…
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Boosted Premixed-LTGC / HCCI Combustion of EHN-doped Gasoline for Engine Speeds Up to 2400 rpm

SAE International Journal of Engines

Chevron Energy Technology Company-William Cannella
Sandia National Laboratories-Chunsheng Ji, John Dec, Jeremie Dernotte
  • Journal Article
  • 2016-01-2295
Published 2016-10-17 by SAE International in United States
Previous work has shown that conventional diesel ignition improvers, 2-ethylhexyl nitrate (EHN) and di-tert-butyl peroxide (DTBP), can be used to enhance the autoignition of a regular-grade E10 gasoline in a well premixed low-temperature gasoline combustion (LTGC) engine, hereafter termed an HCCI engine, at naturally aspirated and moderately boosted conditions (up to 180 kPa absolute) with a constant engine speed of 1200 rpm and a 14:1 compression ratio. In the current work the effect of EHN on boosted HCCI combustion is further investigated with a higher compression ratio (16:1) piston and over a range of engine speeds (up to 2400 rpm). The results show that the higher compression ratio and engine speeds can make the combustion of a regular-grade E10 gasoline somewhat less stable. The addition of EHN improves the combustion stability by allowing combustion phasing to be more advanced for the same ringing intensity. The high-load limits of both the straight (unadditized) and additized fuels are determined, and the additized fuel is found to achieve a higher maximum load at all engine speeds and intake…
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