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Zirconium dioxide (ZrO2) doped with Yttria exhibits superplastic behaviour, corrosion resistance and excellent ion conducting properties [1] at moderate temperatures and thus it can be used as an electroceramic to measure the pH of high temperature water used in fuel cells. Several fabrication processes are available for preparation of zirconia ceramics. This research focused on the study of using Spark Plasma Sintering (SPS) process to prepare Yttria Stabilized Zirconia (YSZ) ceramic. 8 mol% YSZ was subjected to varying SPS sintering conditions. Samples were sintered by changing the heating cycle, dwell time, sintering pressure and cooling cycle. Subsequently, these parameters were related to the densification characteristics of the as-sintered YSZ. The results of specific gravity measurements and microstructure evaluation suggest that stepped heating followed by a slow cooling results in YSZ with highest relative density (99.9%).

Multidimensional simulations are being used to assist the development of a directly injected natural gas system for heavy-duty diesel engines. In this method of converting diesel engines to natural gas fueling, the gas injection takes place at high pressure at the end of the compression stroke. A small amount of pilot diesel fuel is injected prior to the natural gas to promote ignition. Both fuels are injected through a centrally located injector. The mathematical simulations are sought to provide a better understanding of the injection and combustion process of pilot-ignited directly-injected natural gas. The mathematical simulations are also expected to help optimize the injection process, looking in particular at the tip geometry and at the injection delay between the two fuels. The paper presents the mathematical model, which is based on the KIVA-II code. The model includes modifications for underexpanded natural gas jets, and includes a turbulent combustion model.

An experimental investigation of the autoignition and emission characteristics of transient turbulent gaseous fuel jets in heated and compressed air was conducted in a shock tube facility. Experiments were performed at an initial pressure of 30 bar with initial oxidizer temperatures ranging from 1200 to 1400 K, injection pressures ranging from 60 to 150 bar, and injection durations ranging from 1.0 to 2.5 ms. Methane and 90.0% methane/10.0% ethane blend were used as fuel. Under the operating conditions studied, increasing temperature resulted in a significant decrease in autoignition delay time. Increasing the injection pressure decreased ignition delay as well. The downstream location of the ignition kernel relative to the jet penetration distance was found to be in the range, 0.4

Soot emissions from direct-injection engines are sensitive to the fuel-air mixing process, and may vary between combustion cycles due to turbulence and injector variability. Conventional exhaust emissions measurements cannot resolve inter- or intra-cycle variations in particle emissions, which can be important during transient engine operations where a few cycles can disproportionately affect the total exhaust soot. The Fast Exhaust Nephelometer (FEN) is introduced here to use light scattering to measure particulate matter concentration and size near the exhaust port of an engine with a time resolution of better than one millisecond. The FEN operates at atmospheric pressure, sampling near the engine exhaust port and uses a laser diode to illuminate a small measurement volume. The scattered light is focused on two amplified photodiodes.

As global energy demands continue to be met with ever evolving and stricter emissions requirements, natural gas (NG) has become a highly researched alternative to conventional fossil fuels in many industrial sectors. Transportation is one such field that can utilize the benefits of NG as a primary fuel for use in internal combustion engines (ICEs). In the context of heavy-duty on-highway transportation applications, diesel-ignited dual-fuel (DIDF) combustion of NG has been identified as a commercially viable alternative technology. Previous investigations of DIDF have examined the various trends present across the spectrum of DIDF operating space. However, in-cylinder processes are still not well understood and this investigation aims to further understanding in this area. An in-cylinder, local infrared absorption fuel concentration sensor is used to examine in-cylinder processes by comparison with previous optical and thermodynamic studies.

Alternative fuel injection systems and advanced in-cylinder diagnostics are two important tools for engine development; however, the rapid and simultaneous achievement of these goals is often limited by the space available in the cylinder head. Here, a research-oriented cylinder head is developed for use on a single cylinder 2-litre engine, and permits three simultaneous in-cylinder combustion diagnostic tools (cylinder pressure measurement, infrared absorption, and 2-color pyrometry). In addition, a modular injector mounting system enables the use of a variety of direct fuel injectors for both gaseous and liquid fuels. The purpose of this research-oriented cylinder head is to improve the connection between thermodynamic and optical engine studies for a wide variety of combustion strategies by facilitating the application of multiple in-cylinder diagnostics.

A Large Eddy Simulation (LES) numerical study of the Partially Stratified Charge (PSC) combustion process is here proposed, carried out with the open Source code OpenFOAM, in a Constant Volume Combustion Chamber (CVCC). The solver has already been validated in previous papers versus experimental data under a limited range of operating conditions. The operating conditions domain for the model validation is extended in this paper, mostly by varying equivalence ratio, to better highlight the influence of turbulence on flame front propagation. Effects of grid sizing are also shown, to better emphasize the trade-off between the level of accuracy of turbulent vortex description, and their impact on the kinematics of flame propagation. Results show the validity of the approach that is evident by comparing numerical and experimental data.

Diesel-ignited dual-fuel (DIDF) combustion of natural gas (NG) is a promising strategy to progress the application of NG as a commercially viable compression ignition engine fuel. Port injection of gaseous NG applied in tandem with direct injection of liquid diesel fuel as an ignition source permits a high level of control over cylinder charge preparation, and therefore combustion. Across the broad spectrum of possible combustion conditions in DIDF operation, different fundamental mechanisms are expected to dominate the fuel conversion process. Previous investigations have advanced the understanding of which combustion mechanisms are likely present under certain sets of conditions, permitting the successful modeling of DIDF combustion for particular operating modes. A broader understanding of the transitions between different combustion modes across the spectrum of DIDF warrants further effort.

The effects of impinging airflow on the near nozzle characteristics of an inwardly opening, high pressure-swirl atomiser are investigated in an optically-accessed, steady-state flow rig designed to emulate the intake flow of a typical, side-injected, 4-valve gasoline direct-injection combustion system. The results indicate that the impinging airflow has a relatively minor effect on the initial break-up of the fuel spray. However, the secondary break-up of the spray, i.e. the break-up of liquid ligaments, the spatial distribution of droplets within the spray and the location of the spray within the cylinder are significantly affected by the impinging air.

An experimental investigation of the autoignition of transient gaseous fuel jets in heated and compressed air is conducted in a shock tube facility. Experiments are performed at an initial pressure of 30 bar with initial oxidizer temperatures ranging from 1150 K to 1400 K, injection pressures ranging from 60 bar to 150 bar, and with injector tip orifice diameters of 0.275 mm and 1.1 mm. Under the operating conditions studied, increasing temperature results in a significant decrease in autoignition delay time, td. The smaller orifice results in an increase in ignition delay time and variability, as compared with the larger orifice. For initial temperatures below about 1250K, ignition is rarely achieved with the smaller orifice, whereas ignition is always achieved with the larger orifice down to 1150 K. Under the conditions studied, increasing the injection pressure decreases ignition delay, a result dynamically consistent with larger orifice size decreasing ignition delay time.

Operators of natural gas engines, used for both mobile and stationary applications, are increasingly looking at running these engines under very lean air-fuel ratios in order to reduce exhaust emissions and increase thermal efficiency. Lean operation of homogeneous-charge spark-ignited engines reduces peak combustion temperatures, thereby reducing NOx emissions. Lean operation is normally restricted, however, by the “lean-limit” of combustion, as measured by the air-fuel ratio above which ignition is impossible, or combustion is incomplete. Operation under lean conditions also reduces the mixture burning rate, which can lead to increased spark advance and lower thermal efficiency. In order to increase the burning rate under ultra-lean air-fuel ratios a new “Squish-Jet” combustion chamber concept has been developed.

High-pressure direct-injection (HPDI) in heavy duty engines allows a natural gas (NG) engine to maintain diesel-like performance while deriving most of its power from NG. A small diesel pilot injection (5-10% of the fuel energy) is used to ignite the direct injected gas jet. The NG burns in a predominantly non-premixed combustion mode which can produce particulate matter (PM). Here we study the effect of injection strategies on emissions from a HPDI engine in two parts. Part-I will investigates the effect of late post injection (LPI) and Part II will study the effect of slightly premixed combustion (SPC) on emission and engine performance. PM reductions and tradeoffs involved with gas late post-injections (LPI) was investigated in a single-cylinder version of a 6-cylinder,15 liter HPDI engine. The post injection contains 10-25% of total fuel mass, and occurs after the main combustion event.

High-pressure direct-injection (HPDI) in heavy duty engines allows a natural gas (NG) engine to maintain diesel-like performance while deriving most of its power from NG. A small diesel pilot injection (5-10% of the fuel energy) is used to ignite the direct injected gas jet. The NG burns in a predominantly mixing-controlled combustion mode which can produce particulate matter (PM). Here we study the effect of injection strategies on emissions from a HPDI engine in two parts. Part-I investigated the effect of late post injection (LPI); the current paper (Part-II) reports on the effects of slightly premixed combustion (SPC) on emission and engine performance. In SPC operation, the diesel injection is delayed, allowing more premixing of the natural gas prior to ignition. PM reductions and tradeoffs involved with gas slightly premixed combustion was investigated in a single-cylinder version of a 6-cylinder, 15 liter HPDI engine.

Compression ignition engines, including those that use natural gas as the major fuel, produce emissions of NOx and particulate matter (PM). Westport Inc. has developed the pilot-ignited high-pressure direct-injection (HPDI) natural gas engine system. Although HPDI engines produce less soot than comparable conventional diesel engines, further reductions in engine-out soot emissions is desired. In diesel engines, multiple injections can help reduce both NOx and PM. The effect of post injections on HPDI engines was not studied previously. The present research shows that late injection of a second gas pulse can significantly reduce PM and CO from HPDI engines without significantly increasing NOx or fuel consumption. In-cylinder pressure measurements were used to characterize the heat release resulting from the multiple injections. Experiments showed that most close-coupled split injection strategies provided no significant emissions benefit and less stable operation.

A diesel pilot-ignited, high-pressure direct-injection of natural gas heavy-duty single-cylinder engine was fuelled with both natural gas and blends of 10% and 23% by volume hydrogen in methane. A single operating condition (6 bar GIMEP, 0.5 ϕ, 800 RPM, 40%EGR) was selected, and the combustion phasing was varied from advanced (mid-point of combustion at top-dead-center) to late (mid-point of combustion at 15°ATDC). Replacing the natural gas with hydrogen/methane blend fuels was found to have a significant influence on engine emissions and on combustion stability. The use of 10%hydrogen was found to slightly reduce PM, CO, and tHC emissions, while improving combustion stability. 23%hydrogen was found to substantially reduce CO and tHC emissions, while slightly increasing NOx. The greatest reductions in CO and tHC, along with a significant reduction in PM, were observed at the latest combustion timings, where combustion stability was lowest.

The paper presents results of an organized and extensive wind tunnel test-program, complemented by flow visualization and full-scale road tests, aimed at assessing the effectiveness of a boundary-layer control procedure for the drag reduction of a cube-van. Wind tunnel results, obtained using 1/6 scale model, at a subcritical Reynolds number of 105, suggest that tripping of the boundary-layer using fences reduce the pressure drag coefficient. The entirely passive character of the procedure is quite attractive from the economic consideration as well as the ease of implementation. The road tests with a full-size cube-van substantiated the trends indicated by the fence data; although the actual drag reduction observed was lower (yet quite significant, 16.6%) than that predicted by the wind tunnel tests. This may be attribute to a wide variety of factors including the differences in the geometry and test conditions. Fuel consumption results also substantiated the drag reduction trend.

High pressure injection of natural gas is being investigated as a mean of fueling diesel engines and meeting increasingly stringent EPA regulations on emissions of nitrogen oxides and particulates. In the work described in this paper, the penetration into air of a sonic jet of methane emerging from a suddenly opened poppet valve has been modelled analytically and measured using flow visualization. The injection pressure ratios were in the range 1.5 to 5 and the conical jet sheet Reynolds numbers were in the range 7000 to 56000. Schlieren photographs revealed that the conical sheet gas jet exhibits an unstable behaviour between the upper and lower plates which simulate the fire deck and the piston. The integral model developed indicates the principal parameters on which the gaseous jet penetration depends and establishes the requirements for scaling. The conical sheet jet penetration is found to be approximately 30% less than that of round holes, given the same flow area.

Impending Environmental Protection Agency (EPA) regulations will place severe limits on exhaust emissions of heavy duty diesel engines for urban bus and highway truck applications. To meet this challenge an intensifier-injector system for natural gas fueling of diesel engines is being developed. The intensifier-injector concept employs electronically-controlled, late-cycle, direct injection of high-pressure natural gas with a pilot quantity of diesel fuel. Preliminary performance and emissions data are presented to indicate the potential for diesel engine efficiencies with reduced emissions with this method of natural-gas fueling.

A new injector has been designed for sequential injection of high-pressure natural gas and a quantity of liquid diesel fuel directly into diesel engine cylinders late in the compression stroke. Injected a few degrees before the natural gas, the pilot liquid fuel auto-ignites and serves, as it burns, to ignite the gaseous fuel which enters the chamber as an underexpanded sonic jet generating high local turbulence. Tests on a single-cylinder two-stroke engine with full electronic control have demonstrated the capability of this fueling method to nearly match conventional diesel engine efficiency over a wide range of load and substantially reduce the emissions of oxides of nitrogen (NOx), particulate mater (PM) and carbon dioxide (CO2).

In this paper a study of the squish-generated charge motion in the combustion chamber of a natural gas engine is reported. A combination of both numerical simulations and actual engine tests was used to correlate the turbulence level at the spark plug location with performance and cylinder pressure data for three different chamber configurations. The higher-turbulence combustion chamber showed an average 1.5% reduction in brake specific fuel consumption in comparison with the lower turbulence level combustion chambers. The emission levels from the high-turbulence case were, however, generally higher than those from the lower-turbulence combustion chambers.