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Journal Article

Uncertainty Assessment of Octane Index Framework for Stoichiometric Knock Limits of Co-Optima Gasoline Fuel Blends

Abstract This study evaluates the applicability of the Octane Index (OI) framework under conventional spark ignition (SI) and “beyond Research Octane Number (RON)” conditions using nine fuels operated under stoichiometric, knock-limited conditions in a direct injection spark ignition (DISI) engine, supported by Monte Carlo-type simulations which interrogate the effects of measurement uncertainty. Of the nine tested fuels, three fuels are “Tier III” fuel blends, meaning that they are blends of molecules which have passed two levels of screening, and have been evaluated to be ready for tests in research engines. These molecules have been blended into a four-component gasoline surrogate at varying volume fractions in order to achieve a RON rating of 98. The molecules under consideration are isobutanol, 2-butanol, and diisobutylene (which is a mixture of two isomers of octene). The remaining six fuels were research-grade gasolines of varying formulations.
Journal Article

The Effect of Inlet Valve Timing and Engine Speed on Dual Fuel NG-Diesel Combustion in a Large Bore Engine

Abstract High load (18 bar IMEP) dual fuel combustion of a premixed natural gas/air charge ignited by directly injected diesel fuel was studied in a large bore gas engine. A nozzle design with low flow rate was installed to inject a small diesel volume (10.4 mm3) equal an energetic amount of about two percent. The effect of compression end temperature on ignition and combustion was investigated using valve timings with early IVC (Miller) and maximum charging efficiency (MaxCC). Furthermore, the engine speed was reduced (1500 rpm to 1000 rpm) for the Miller valve timing to analyze the impact of the chemical time scale on the combustion process. During all experiments, the cylinder charge density was kept constant adjusting the intake pressure and the resulting air mass flow.
Journal Article

Performance, Fuel Economy, and Economic Assessment of a Combustion Concept Employing In-Cylinder Gasoline/Natural Gas Blending for Light-Duty Vehicle Applications

Abstract In current production natural gas/gasoline bi-fuel vehicles, fuels are supplied via port fuel injection (PFI). Injecting a gaseous fuel in the intake port significantly reduces the volumetric efficiency and consequently torque as compared to gasoline. In addition to eliminating the volumetric efficiency challenge, direct injection (DI) of natural gas (NG) can enhance the in-cylinder flow, mixing, and combustion process resulting in improved efficiency and performance. A computational fluid dynamics (CFD) approach to model high-pressure gaseous injection was developed and validated against X-ray data from Argonne’s Advanced Photon Source. NG side and central DI of various designs and injection strategies were assessed experimentally along with CFD correlation. Significant effects on combustion metrics were quantified and explained via improved understanding of the in-cylinder flow effects due to NG injection.
Journal Article

Literature Review on the Effects of Organometallic Fuel Additives in Gasoline and Diesel Fuels

Abstract A literature review was conducted and fuel survey data were obtained to identify the use of metallic fuel additives (MFAs) within market fuels and determine their effects on engines, exhaust systems, and vehicle performance. The primary focus was on modern vehicles equipped with on-board diagnostic (OBD) systems and advanced emissions control systems. For gasoline, this includes vehicles categorized as National Low Emission Vehicles (NLEV) and Tier 2 or beyond in the U.S., and Euro-3 through Euro-6 in the EU. For diesel, this includes engines/vehicles with original equipment manufacturer (OEM)-equipped oxidation catalysts and diesel particulate filters. The literature search of peer-reviewed papers and other publicly available articles returned over 100 items relevant to the use of organometallic fuel additives, but did not provide significant evidence of widespread use of MFAs in either gasoline or diesel fuels.
Journal Article

LSPI Durability, a Study of LSPI over the Life of a Vehicle

Abstract Increasingly stringent emissions standards and the related efforts to increase vehicle fuel economy have forced the development and implementation of many new technologies. In the light-duty, passenger vehicle segment, one key strategy has been downsized, down-sped, boosted engines. Gasoline direct injection, coupled with turbocharging, have allowed for a drastic reduction in engine size while maintaining or improving engine performance. However, obtaining more power from a smaller engine has produced some consequences. One major consequence is the uncontrolled combustion known as Low Speed Pre-Ignition (LSPI). LSPI and the high energy knocking event which frequently follows have been known to result in fractured pistons and catastrophic engine failure. The propensity at which LSPI occurs has been linked to engine oil formulation.
Journal Article

Knock Phenomena under Very Lean Conditions in Gasoline Powered SI-Engines

Abstract Homogeneous lean operation is a well-known strategy for enhancing the thermal efficiency of SI-engines. At higher load points the efficiency is often compromised by the need to suppress knock. Experiments were performed to determine the knock characteristics of SI engines using homogeneous lean operation at λ values of up to 1.8 with various hardware configurations that are commonly used to increase the lean limit. Changing λ altered the eigenfrequencies of the combustion chamber and the highest energy excitation mode. Increasing λ from 1.0 to 1.2 increased the knock tendency and led to an earlier knock onset. However, further increases in λ significantly reduced the knock tendency and retarded the knock onset. The knock signal energy increased for higher λ values and constant knock tendencies. The differences in knock characteristics between the various λ values became more pronounced upon raising the intake temperature from 40 °C to 90 °C.
Journal Article

High Power-Density, High Efficiency, Mechanically Assisted, Turbocharged Direct-Injection Jet-Ignition Engines for Unmanned Aerial Vehicles

Abstract More than a decade ago, we proposed combined use of direct injection (DI) and jet ignition (JI) to produce high efficiency, high power-density, positive-ignition (PI), lean burn stratified, internal combustion engines (ICEs). Adopting this concept, the latest FIA F1 engines, which are electrically assisted, turbocharged, directly injected, jet ignited, gasoline engines and work lean stratified in a highly boosted environment, have delivered peak power fuel conversion efficiencies well above 46%, with specific power densities more than 340 kW/liter. The concept, further evolved, is here presented for unmanned aerial vehicle (UAV) applications. Results of simulations for a new DI JI ICE with rotary valve, being super-turbocharged and having gasoline or methanol as working fuel, show the opportunity to achieve even larger power densities, up to 430 kW/liter, while delivering a near-constant torque and, consequently, a nearly linear power curve over a wide range of speeds.
Journal Article

Gasoline Particulate Filter Wall Permeability Testing

Abstract With the introduction of particulate matter emissions regulations for gasoline engines, most car manufacturers are considering using gasoline particulate filters (GPFs). Although very similar to diesel particulate filters (DPFs), GPFs operate at higher temperatures and generally have thinner monolith walls. In order to estimate the pressure loss through the filter, filter wall permeability is needed. This presents a number of challenges since wall losses cannot be efficiently isolated from other losses in a full-scale filter or filter core. Thin wall wafers have been used for DPF characterization. However, GPF wafers are generally thinner, which makes the testing less straightforward. This article presents a novel effective methodology for estimation of GPF wall permeability using thin wafers cut from the filter monolith. Both cold and hot flow permeabilities can be estimated, which allows to account for the change of apparent permeability due to the slip effect.
Journal Article

Gasoline Fueled Pre-Chamber Ignition System for a Light-Duty Passenger Car Engine with Extended Lean Limit

Abstract In this work, a light-duty research engine based on a passenger car engine is equipped with an in-house developed pre-chamber (PC) ignition system replacing the conventional spark plug. By using such kind of ignition system, the combustion in the main chamber is enhanced by radical seeding through jets travelling from the pre-chamber to the main chamber. These radicals serve as high-energy ignition sites for the mixture in the main combustion chamber leading to enhanced burn rates and combustion speed. In contrast to conventional spark-ignited combustion starting from the spot of the electrode gap, an extended lean misfire limit and a mitigated knocking tendency are achieved. The presence of a gasoline direct injector inside the PC enables the system to operate in both passive and active modes. The injection of a small fuel amount allows separating the air-to-fuel equivalence ratio of the pre-chamber and the main chamber.
Journal Article

Exploring Engine Oil Reactivity Effects on End Gas Knock in a Direct-Injection Spark Ignition Engine

Abstract An experimental study was conducted in a direct-injection (DI) spark-ignited engine to determine the extent to which oil reactivity impacts combustion phasing and knock propensity. Three engine oils were examined: a baseline 20W30 oil from conventional base stock, a 5W30 oil from a synthetic base stock, and a jet oil from a hindered ester base stock. The engine was operated at a constant fueling rate of 24.7 mg/injection for two engine speed conditions (1500 and 2000 rpm) using two cam profile conditions (high and low lift), for a total of four operating conditions. Spark timing sweeps were conducted at each of the four operating conditions. Results were analyzed for an engine oil impact on combustion phasing, cycle-to-cycle variability, combustion duration, knock propensity, and knock intensity. No correlation between engine oil type and any of these performance metrics could be identified.
Journal Article

Diminishing Benefits of Federal Reformulated Gasoline (RFG) Compared to Conventional Gasoline (CG)

Abstract The Federal reformulated gasoline (RFG) program originated with the 1990 Clean Air Act Amendments to address high ozone and air toxics levels in major urban areas. These areas include portions of 17 states and represent approximately 30% of the total U.S. gasoline volume. Initially, formulation changes were limited to addition of oxygen and reductions in benzene and fuel Reid vapor pressure (RVP) levels. These reformulations were intended to meet minimum emissions reduction targets for volatile organic compounds (VOCs), air toxics, and oxides of nitrogen (NOx) when compared to a 1990 baseline gasoline in a “1990’s technology” vehicle fleet. The United States Environmental Protection Agency (U.S. EPA) developed two computational models, the Simple Model in 1995 and the Complex Model in 1998, for use in demonstrating compliance with the regulations. This article reviews the derivation and evolution of the RFG program.
Journal Article

Carbon Monoxide Density Pattern Mapping from Recreational Boat Testing

Abstract Exposure to carbon monoxide (CO) gas can cause health risks for users of recreational boats and watercraft. Activities such as waterskiing, wakeboarding, tubing, and wakesurfing primarily utilize gasoline engine-driven vessels which produce CO as a combustion by-product. Recent watersports trends show an increase in popularity of activities which take place closer to the stern of the boat (such as wakesurfing) as compared to traditional waterskiing and wakeboarding. Advancements in gas emissions treatment in marine engine exhaust system designs have reduced risks for CO exposure in some boats. This article presents results from on-water testing of three recreational boats, reports average and maximum values of CO levels under various conditions, and exhibits mapping of the density of CO relative to the stern of the test vessels.
Journal Article

A Study of Low Temperature Plasma-Assisted Gasoline HCCI Combustion

Abstract In this study low temperature plasma technology was applied to expand auto-ignition operation region and control auto-ignition phasing of the homogeneous charge compression ignition (HCCI) combustion. The low temperature plasma igniter of a barrier discharge model (barrier discharge igniter (BDI)) with high-frequency voltage (15 kHz) was provided at the top center of the combustion chamber, and the auto-ignition characteristics of the HCCI combustion by the low temperature plasma assistance was investigated by using a single-cylinder gasoline engine. HCCI combustion with compression ratio of 15:1 was achieved by increasing the intake air temperature. The lean air-fuel (A/F) ratio limit and visualized auto-ignition combustion process on baseline HCCI without discharge assistance, spark-assisted HCCI, and BDI-assisted HCCI were compared.