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Ethanol blending is one method that can be used to reduce knock in spark ignition engines by decreasing the autoignition reactivity of the fuel and modifying its laminar flame speed. In this paper, the effects of ethanol blending on knock propensity and flame speed of petroleum and low-carbon gasoline fuels is analyzed. To do so, surrogate fuels were formulated for methanol-to-gasoline (MTG) and ethanol-to-gasoline (ETG) based on the fuels’ composition, octane number, and select physical properties; and 0-D and 1-D chemical kinetics simulations were performed to investigate reactivity and laminar flame speed, respectively. Results of MTG and ETG were compared against those of PACE-20, a well-characterized surrogate for regular E10 gasoline. Similarly to PACE-20, blending MTG and ETG with ethanol increases the fuel’s research octane number (RON) and sensitivity.

Methanol emerges as a compelling renewable fuel for decarbonizing engine applications due to a mature industry with high production capacity, existing distribution infrastructure, low carbon intensity and favorable cost. Methanol’s high flame speed and high autoignition resistance render it particularly well-suited for spark-ignition (SI) engines. Previous research showed a distinct phenomenon, known deflagration-based knock in methanol combustion, whereby knocking combustion was observed albeit without end-gas autoignition. This work studies the implications of deflagration-based knock on noise emissions by investigating the knock intensity and combustion noise at knock-limited operation of methanol in a single-cylinder direct-injection SI engine operated at both stoichiometric and lean (λ = 2.0) conditions. Results are compared against observations from a premium-grade gasoline.

Surrogate fuels that reproduce the characteristics of full-boiling range fuels are key tools to enable numerical simulations of fuel-related processes and ensure reproducibility of experiments by eliminating batch-to-batch variability. Within the PACE initiative, a surrogate fuel for regular-grade E10 (10%vol ethanol) gasoline representative of a U.S. market gasoline, termed PACE-20, was developed and adopted as baseline fuel for the consortium. Although extensive testing demonstrated that PACE-20 replicates the properties and combustion behavior of the full-boiling range gasoline, several concerns arose regarding the purity level required for the species that compose PACE-20. This is particularly important for cyclo-pentane, since commercial-grade cyclo-pentane typically shows 60%–85% purity. In the present work, the effects of the purity level of cyclo-pentane on the properties and combustion characteristics of PACE-20 were studied.

Renewably sourced hydrogen is seen as promising sustainable carbon-free alternative to conventional fossil fuels for use in hard to decarbonize sectors. As the hydrogen supply builds up, dual-fuel hydrogen-diesel engines have a particular advantage of fuel flexibility as they can operate only on diesel fuel in case of supply shortages, in addition to the simplicity of engine modification. The dual-fuel compression ignition strategy initiates combustion of hydrogen using short pilot-injections of diesel fuel into the combustion chamber. In the context of such engine combustion process, the impact of hydrogen addition on the ignition and combustion behavior of a pilot diesel-spray is investigated in a heavy-duty, single-cylinder, optical engine. To this end, the spatial and temporal evolution of two-stage autoignition of a diesel-fuel surrogate, n-heptane, injected into a premixed charge of hydrogen and air is studied using optical diagnostics.

Despite recent advances towards powertrain electrification as a solution to mitigate pollutant emissions from road transport, synthetic fuels (especially e- fuels) still have a major role to play in applications where electrification will not be viable in short-medium term. Among e-fuels, oxymethylene ethers are getting serious interest within the scientific community and industry. Dimethoxy methane (OME1) is the smaller molecule among this group, which is of special interest due to its low soot formation. However, its application is still limited mainly due to its low lower heating value. In contrast, other fuel alternatives like hydrogenated vegetable oil (HVO) are considered as drop-in solutions thanks to their very similar properties and molecular composition to that of fossil diesel. However, their pollutant emission improvement is limited.

Autoignition enhancing additives have been used for years to enhance the ignition quality of diesel fuel, with 2-ethylhexyl nitrate (EHN) being the most common additive. EHN also enhances the autoignition reactivity of gasoline, which has advantages for some low-temperature combustion techniques, such as Sandia’s Low-Temperature Gasoline Combustion (LTGC) with Additive-Mixing Fuel Injection (AMFI). LTGC-AMFI is a new high-efficiency and low-emissions engine combustion process based on supplying a small, variable amount of EHN into the fuel for better engine operation and control. However, the mechanism by which EHN interacts with the fuel remains unclear. In this work, a chemical-kinetic mechanism for EHN was developed and implemented in a detailed mechanism for gasoline fuels. The combined mechanism was validated against shock-tube experiments with EHN-doped n-heptane and HCCI engine data for EHN-doped regular E10 gasoline. Simulations showed a very good match with experiments.

The spatial and temporal locations of autoignition depend on fuel chemistry and the temperature, pressure, and mixing trajectories in the fuel jets. Dual-fuel systems can provide insight into fuel-chemistry aspects through variation of the proportions of fuels with different reactivities, and engine operating condition variations can provide information on physical effects. In this context, the spatial and temporal progression of two-stage autoignition of a diesel-fuel surrogate, n-heptane, in a lean-premixed charge of synthetic natural gas (NG) and air is imaged in an optically accessible heavy-duty diesel engine. The lean-premixed charge of NG is prepared by fumigation upstream of the engine intake manifold.

Low-temperature gasoline combustion engines can provide high efficiencies with very low NOx and particulate emissions, but rapid control of the combustion timing (50% burn point, CA50) remains a challenge. Partial Fuel Stratification (PFS) was recently demonstrated [2019-01-1156] to control CA50 over a wide range at some selected operating conditions using a regular-grade E10 gasoline. PFS was produced by a double direct injection (D-DI) strategy using a gasoline-type direct injector. For this D-DI-PFS strategy, the majority of the fuel is injected early in the intake stroke, establishing the minimum equivalence ratio in the charge, while the remainder of the fuel is supplied by a second injection at a variable time (SOI2) during the compression stroke to vary the amount of stratification. Adjusting the stratification changes the combustion timing, and this can be done on a cycle-to-cycle basis by adjusting SOI2.

Fuel-lean combustion using late injection during the compression stroke can result in increased soot emissions due to excessive wall-wetting and locally unfavorable air-fuel mixtures due to spray collapse. Multi-hole injectors, most commonly used, experiencing spray collapse, can worsen both problems. Hence, it is of interest to study the contribution of spray collapse to wall-wetting to understand how it can be avoided. This optical-engine study reveals spray characteristics and the associated wall-wetting for collapsing and non-collapsing sprays, when systematically changing the intake pressure, injection duration and timing. High-speed imaging of Mie-scattered light was used to observe changes in the spray structure, and a refractive index matching (RIM) technique was utilized to detect and quantify the area of fuel-film patterns on bottom of the piston bowl. E30 (gasoline blended with 30% ethanol by volume) was used throughout the experiments.

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 not very ϕ-sensitive at low-pressure conditions, meaning that intake boosting (typically Pin ≥ 1.3 bar) is required to take advantage of this property. Thus, there is strong motivation to design a gasoline-like fuel that simultaneously improves ϕ-sensitivity, RON and octane sensitivity, to make an improved fuel suitable for both 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 when it was compared to a regular E10 gasoline (RD5-87). The current study experimentally evaluates CB#1 in the Sandia LTGC engine and compares the results with those of RD5-87. The RON and octane sensitivity were improved 1.3 and 3.6 units by CB#1, respectively.

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.

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.

Mechanisms responsible for enhanced charge reactivity with intake added ozone (O3) were explored in a single-cylinder, optically accessible, research engine configured for low-load advanced compression ignition (ACI) experiments. The influence of O3 concentration (0-40 ppm) on engine performance metrics was evaluated as a function of intake temperature and start of injection for the engine fueled by iso-octane, 1-hexene, or a 5-component gasoline surrogate. For the engine fueled by either the gasoline surrogate or 1-hexene, 25 ppm of added O3 reduced the intake temperature required for stable combustion by 65 and 80°C, respectively. An ultraviolet (UV) light absorption diagnostic was also used to measure crank angle (CA) resolved in-cylinder O3 concentrations for select motored and fired operating conditions. The O3 measurements were compared to results from complementary 0D chemical kinetic simulations that utilized detailed chemistry mechanisms augmented with O3 oxidation chemistry.

Spark-ignition (SI) engine efficiency is typically limited by fuel auto-ignition resistance, which is described in practice by the Research Octane Number (RON) and the Motor Octane Number (MON). The goal of this work is to assess whether fuel properties (i.e. RON, MON, and heat of vaporization) are sufficient to describe the antiknock behavior of varying gasoline formulations in modern engines. To this end, the auto-ignition resistance of three compositionally dissimilar gasoline-like fuels with identical RON values and varying or non-varying MON values were evaluated in a modern, prototype, 12:1 compression ratio, high-swirl (by nature of intake valve deactivation), directly injected spark ignition (DISI) engine at 1400 RPM. The three gasolines are an alkylate blend (RON=98, MON=97), a blend with high aromatic content (RON=98, MON=88), and a blend of 30% ethanol by volume with a gasoline BOB (RON=98, MON=87; see Table 2 for details).

Fuel reforming during a Negative Valve Overlap (NVO) period is an effective approach to control Low Temperature Gasoline Combustion (LTGC) ignition. Previous work has shown through experiments that primary reference fuels reform easily and produce several species that drastically affect ignition characteristics. However, our previous research has been unable to accurately predict measured reformate composition at the end of the NVO period using simple single-zone models. In this work, we use a stochastic reactor model (SRM) closed cycle engine simulation to predict reformate composition accounting for in-cylinder temperature and mixture stratification. The SRM model is less computationally intensive than CFD simulations while still allowing the use of large chemical mechanisms to predict intermediate species formation rates.

In-cylinder reforming of injected fuel during an auxiliary negative valve overlap (NVO) period can be used to optimize main-cycle auto-ignition phasing for low-load Low-Temperature Gasoline Combustion (LTGC), where highly dilute mixtures can lead to poor combustion stability. When mixed with fresh intake charge and fuel, these reformate streams can alter overall charge reactivity characteristics. The central issue remains large parasitic heat losses from the retention and compression of hot exhaust gases along with modest pumping losses that result from mixing hot NVO-period gases with the cooler intake charge. Accurate determination of total cycle energy utilization is complicated by the fact that NVO-period retained fuel energy is consumed during the subsequent main combustion period. For the present study, a full-cycle energy analysis was performed for a single-cylinder research engine undergoing LTGC with varying NVO auxiliary fueling rates and injection timing.

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.

Well-mixed lean or dilute SI engine operation can provide efficiency improvements relative to that of traditional well-mixed stoichiometric SI operation. However, the realized gains depend on the ability to ensure stable, complete and fast combustion. In this work, the influence of fuel type is examined for gasoline, E30 and E85. Several enabling techniques are compared. For enhanced ignition stability, a multi-pulse (MP) transient plasma ignition system is compared to a conventional high-energy inductive spark ignition system. Combined effects of fuel type and intake-gas preheating are examined. Also, the effects of dilution type (air or N2-simulated EGR) on lean efficiency gains and stability limits are clarified. The largest efficiency improvement is found for lean gasoline operation using intake preheating, showing the equivalent of a 20% fuel-economy gain relative to traditional non-dilute stoichiometric operation.

Negative Valve Overlap (NVO) is a potential control strategy for enabling Low-Temperature Gasoline Combustion (LTGC) at low loads. While the thermal effects of NVO fueling on main combustion are well-understood, the chemical effects of NVO in-cylinder fuel reforming have not been extensively studied. The objective of this work is to examine the effects of fuel molecular structure on NVO fuel reforming using gas sampling and detailed speciation by gas chromatography. Engine gas samples were collected from a single-cylinder research engine at the end of the NVO period using a custom dump-valve apparatus. Six fuel components were studied at two injection timings: (1) iso-octane, (2) n-heptane, (3) ethanol, (4) 1-hexene, (5) cyclohexane, and (6) toluene. All fuel components were studied neat except for toluene - toluene was blended with 18.9% nheptane by liquid volume to increase the fuel reactivity.

With the introduction of more fuel cell electric vehicles (FCEVs) on U.S. roadways, especially in California, the need for available hydrogen refueling stations is growing. While funding from the California Energy Commission is helping to solve this problem, solutions need to be developed and implemented to help reduce the time to commission a hydrogen station. The current practice of hydrogen station acceptance can take months because each vehicle manufacturer conducts their own testing and evaluation. This process is not practical or sufficient to support the timely development of a hydrogen fueling station network. To address this issue, as part of the Hydrogen Fueling Infrastructure Research and Station Technology (H2FIRST) Project Sandia National Laboratories and the National Renewable Energy Laboratory along with a team of stakeholders and contractor Powertech Labs has developed the Hydrogen Station Equipment Performance (HyStEP) Device.