Accommodation requirements for microgravity science and applications research on space station

Scientific research conducted in the microgravity environment of space represents a unique opportunity to explore and exploit the benefits of materials processing in the virtual abscence of gravity induced forces. NASA has initiated the preliminary design of a permanently manned space station that will support technological advances in process science and stimulate the development of new and improved materials having applications across the commercial spectrum. A study is performed to define from the researchers' perspective, the requirements for laboratory equipment to accommodate microgravity experiments on the space station. The accommodation requirements focus on the microgravity science disciplines including combustion science, electronic materials, metals and alloys, fluids and transport phenomena, glasses and ceramics, and polymer science. User requirements have been identified in eleven research classes, each of which contain an envelope of functional requirements for related experiments having similar characteristics, objectives, and equipment needs. Based on these functional requirements seventeen items of experiment apparatus and twenty items of core supporting equipment have been defined which represent currently identified equipment requirements for a pressurized laboratory module at the initial operating capability of the NASA space station

Analysis of controlled auto-ignition /HCCI combustion in a direct injection gasoline engine with single and split fuel injections

A multi-cycle three-dimensional CFD engine simulation programme has been developed and applied to analyze the Controlled autoignition (CAI) combustion, also known as homogeneous charge compression ignition (HCCI), in a direct injection gasoline engine. CAI operation was achieved through the negative valve overlap method by means of a set of low lift camshafts. In the first part of the paper, the effect of single injection timing on combustion phasing and underlying physical and chemical processes involved was examined through a series of analytical studies using the multi-cycle 3D engine simulation programme. The analyses showed that early injection into the trapped burned gases of a lean-burn mixture during the negative valve overlap period had a large effect on combustion phasing, due to localized heat release and the production of chemically reactive species. As the injection was retarded to the intake stroke, the charge cooling effect tended to slow down the autoignition process. However, further retard of fuel injection to the compression stroke caused the earlier start of main combustion as fuel stratification was produced in the cylinder. In order to optimize the engine performance and engine-out emissions, double injection was investigated by injecting part of the fuel first in the negative valve overlap period and the rest of fuel during the intake or compression strokes. By varying the fueling of each injection, the best engine performance was obtained with the 50/50 fuel injection split ratio, while the lowest total NOx and soot emissions were seen with the optimal split injection ratio of 10/90

Experimental and theoretical study of combustion jet ignition

A combustion jet ignition system was developed to generate turbulent jets of combustion products containing free radicals and to discharge them as ignition sources into a combustible medium. In order to understand the ignition and the inflammation processes caused by combustion jets, the studies of the fluid mechanical properties of turbulent jets with and without combustion were conducted theoretically and experimentally. Experiments using a specially designed igniter, with a prechamber to build up and control the stagnation pressure upstream of the orifice, were conducted to investigate the formation processes of turbulent jets of combustion products. The penetration speed of combustion jets has been found to be constant initially and then decreases monotonically as turbulent jets of combustion products travel closer to the wall. This initial penetration speed to combustion jets is proportional to the initial stagnation pressure upstream of the orifice for the same stoichiometric mixture. Computer simulations by Chorin's Random Vortex Method implemented with the flame propagation algorithm for the theoretical model of turbulent jets with and without combustion were performed to study the turbulent jet flow field. In the formation processes of the turbulent jets, the large-scale eddy structure of turbulence, the so-called coherent structure, dominates the entrainment and mixing processes. The large-scale eddy structure of turbulent jets in this study is constructed by a series of vortex pairs, which are organized in the form of a staggered array of vortex clouds generating local recirculation flow patterns

Thermal and Catalytic Cracking of JP-10 for Pulse Detonation Engine Applications

Practical air-breathing pulse detonation engines (PDE) will be based on storable liquid hydrocarbon fuels such as JP-10 or Jet A. However, such fuels are not optimal for PDE operation due to the high energy input required for direct initiation of a detonation and the long deflagration-to-detonation transition times associated with low-energy initiators. These effects increase cycle time and reduce time-averaged thrust, resulting in a significant loss of performance. In an effort to utilize such conventional liquid fuels and still maintain the performance of the lighter and more sensitive hydrocarbon fuels, various fuel modification schemes such as thermal and catalytic cracking have been investigated. We have examined the decomposition of JP-10 through thermal and catalytic cracking mechanisms at elevated temperatures using a bench-top reactor system. The system has the capability to vaporize liquid fuel at precise flowrates while maintaining the flow path at elevated temperatures and pressures for extended periods of time. The catalytic cracking tests were completed utilizing common industrial zeolite catalysts installed in the reactor. A gas chromatograph with a capillary column and flame ionization detector, connected to the reactor output, is used to speciate the reaction products. The conversion rate and product compositions were determined as functions of the fuel metering rate, reactor temperature, system backpressure, and zeolite type. An additional study was carried out to evaluate the feasibility of using pre-mixed rich combustion to partially oxidize JP-10. A mixture of partially oxidized products was initially obtained by rich combustion in JP-10 and air mixtures for equivalence ratios between 1 and 5. Following the first burn, air was added to the products, creating an equivalent stoichiometric mixture. A second burn was then carried out. Pressure histories and schlieren video images were recorded for both burns. The results were analyzed by comparing the peak and final pressures to idealized thermodynamic predictions

Effective Ignition Control in Advanced Combustion Engines

The primary objective of the research was to study the limitations of the conventional spark ignition architecture with respect to ultra-lean and dilute combustion and develop ignition technologies and strategies that can facilitate such combustion strategies. A range of strategies using conventional and modified ignition coil systems were used in combustion chamber and engine tests to understand the effectiveness of the energy delivery mechanisms and different energy profiles. At operating conditions where the conventional ignition strategies had difficulties in achieving adequate ignition stability, the use of enhanced energy levels with different energy profiles for the achievement of effective ignition under high dilution ratio engine operating conditions was found to be necessary. A novel multiple-site ignition system was developed. It has been demonstrated to effectively deliver of ignition energy and achieved higher tolerance for lean combustion and high-dilution modes of combustion. A radio-frequency non-thermal plasma ignition system was developed to investigate its ability to address some of the deficiencies of the spark ignition architecture. Compared to the conventional spark ignition architecture, the ignition volume induced by the corona discharge was greater in size and its growth was less impeded with the absence of a close ground electrode. The rapid energization and discharge characteristics additionally offered a more flexible control path. The formation of multiple ignition sites was possible, although implementation of the system in the engine environment has proven to be a continuing challenge

Development and Demonstration of Control Strategies for a Common Rail Direct Injection Armoured Fighting Vehicle Engine

The development of a controller which can be used for engines used in armoured fighting vehicles is discussed. This involved choosing a state of the art reference common rail automotive Diesel engine and setting-up of a transient engine testing facility. The dynamometer through special real-time software was controlled to vary the engine speed and throttle position. The reference engine was first tested with its stock ECU and its bounds of operation were identified. Several software modules were developed in-house in stages and evaluated on special test benches before being integrated and tested on the reference engine. Complete engine control software was thus developed in Simulink and flashed on to an open engine controller which was then interfaced with the engine. The developed control software includes strategies for closed loop control of fuel rail pressure, boost pressure, idle speed, coolant temperature based engine de-rating, control of fuel injection timing, duration and number of injections per cycle based on engine speed and driver input. The developed control algorithms also facilitated online calibration of engine maps and manual over-ride and control of engine parameters whenever required. The software was further tuned under transient conditions on the actual engine for close control of various parameters including rail pressure, idling speed and boost pressure. Finally, the developed control strategies were successfully demonstrated and validated on the reference engine being loaded on customised transient cycles on the transient engine testing facility with inputs based on military driving conditions. The developed controller can be scaled up for armoured fighting vehicle engines

Modeling, control, and implementation of enhanced premixed combustion in diesel engines

Three different combustion modes for simultaneous low-nitrogen oxides (NOx) and low-particulate-matter (PM) called enhanced-premixed combustion (EPC) are described in this thesis for diesel engines. a) Multi-pulse EPC: This combustion mode was implemented with multi-pulse fuel-injection events early during the compression stroke and a heavy use of EGR. This type of combustion was characterized by a short combustion duration which increased the rate-of-pressure rise and maximum pressures in comparison to the conventional diesel combustion mode. The combustion phasing for this mode was kinetics controlled and this combustion mode was largely applicable to mid-load engine operating conditions. b) EGR enabled EPC with single injection: This combustion mode was implemented with a single-injection close to top-dead center and a heavy use of EGR. The use of closed-loop control on combustion phasing via a cylinder pressure based control was found to be an important enabler for stabilizing this type of combustion. This combustion mode was applied mainly at low-load engine operating conditions. c) Combustion mode with a split heat-release characteristic: This combustion mode consisted of a part of the fuel delivery very early during the compression stroke and a part of the fuel delivery close to the top-dead-centre (TDC). The part of fuel injected close to TDC experienced conventional high-temperature combustion and oxidized the carbon-monoxide produced earlier in the cycle, thereby improving combustion efficiency. The split nature of the combustion limited the rate-of-pressure rise associated with the multi-pulse EPC combustion. The implementation of EPC were associated with fuel-efficiency penalty either due to off-phasing of combustion event, UHC and carbon-monoxide or oil-dilution. Specific strategies have been presented to overcome each of these limitations. A production version of 2.0 Liter, 4-cylinder FORD common-rail diesel engine was modified for the EPC experiments to run in a single-cylinder mode using a prototype intake and exhaust manifold and using independent fuel-injection strategies

Advanced Ignition Strategies for Future Internal Combustion Engines with Lean and Diluted Fuel-Air Mixtures

The main objective of this research was to study the mechanisms of the spark ignition process of lean or diluted fuel-air mixtures under enhanced gas flow conditions for applications in future internal combustion engines. Various spark ignition strategies were deployed by controlling the spark discharge process via different spark ignition hardware configurations. Modulated spark discharge parameters, such as enhanced discharge power, prolonged discharge duration, and boosted discharge current were facilitated in the research. The impact of gas flow on the spark discharge process in air was investigated under varying air flow conditions with a range of flow velocities from 0 m/s to 60 m/s. The ignition performance of the spark strategies was investigated with lean or diluted fuel-air mixtures under controlled gas flow conditions in an optical constant volume combustion chamber test platform. The mixture flow velocity across the spark gap ranged from 0 m/s to 35 m/s during the combustion tests.Experiments were carried out with air as the background media. Short circuits and restrikes were observed under air flow conditions. The frequency of these occurrences increased with increased air flow velocity. The length of the spark plasma increased, due to the stretch of the plasma channel by the air flow. The plasma was stretched at a speed similar to the air flow velocity across the spark gap. The maximum length of the spark plasma was affected by the air flow velocity and the spark gap size. The spark discharge duration reduced with increased air flow velocity. To enhance the ignition of a lean or diluted fuel-air mixture under quiescent conditions, high spark discharge power or high spark discharge current were applied. With equivalent spark discharge energy, a larger flame kernel was achieved by the high-power spark whereas the impacts of spark discharge current level and discharge duration during the arc and glow phases were insignificant on the flame kernel growth. A transient high-current spark also generated a larger flame kernel, although with much higher spark energy as compared with that from a conventional spark. Under gas flow conditions, both the spark discharge current magnitude and discharge duration were critical for the flame kernel growth. It is postulated that this kernel growth was the result of a prolonged spark discharge duration effectively increasing the interaction volume between the plasma channel and the combustible gas engulfed by the mixture flow. Consequently, a longer spark discharge duration proved beneficial in establishing a larger flame kernel, probably because the spark discharge current was sufficient to support the flame kernel growth. Indeed, it was observed that boosted spark current was advantageous for the flame kernel growth, especially at higher flow velocities. However, the high-power spark and transient high-current spark proved to be less effective with higher flow velocities, probably because of the short discharge duration

Experimental and theoretical investigation of fatigue life in reusable rocket thrust chambers

During a test program to investigate low-cycle thermal fatigue, 13 rocket combustion chambers were fabricated and cyclically test fired to failure. Six oxygen-free, high-conductivity (OFHC) copper and seven Amzirc chambers were tested. The failures in the OFHC copper chambers were not typical fatigue failures but are described as creep rupture enhanced by ratcheting. The coolant channels bulged toward the chamber centerline, resulting in progressive thinning of the wall during each cycle. The failures in the Amzirc alloy chambers were caused by low-cycle thermal fatigue. The zirconium in this alloy was not evenly distributed in the chamber materials. The life that was achieved was nominally the same as would have been predicted from OFHC copper isothermal test data

Injection and combustion analysis and knock detection models for high-efficiency natural gas engines

Between different sectors, GHG emissions released by automotive one in 2010 were 4.5 GtCO2, the 14% of the total (32 GtCO2). Moreover, transport sector depends by more than 93% on oil, to be refined into gasoline and diesel fuel. Natural gas demand in transport sector has clearly increased in the last decade considering the lowest CO2 emissions per units of energy produced among different fossil fuels but it will be used mostly in the next future. Among different sectors, the 21 % of the energy demand is indeed supplied by NG, due to lower price and reduced GHG emissions. Storage type (compressed natural gas or liquefied natural gas) and vehicle type (road transport, marine transport, etc.) mainly discriminate natural gas engine layouts. Spark-ignition natural gas engine with different configurations will be indeed taken into consideration in this research project. Today, vehicles for the road transport fueled with compressed natural gas are mainly bi-fuel ones with both gasoline and natural gas feeding system with a manual or automatic switch. To mitigate knock event, engine layout is designed up to gasoline characteristics and engine performances with natural gas are not fully exploited. Mono-fuel configuration is capable to totally exploit the potential of natural gas. Therefore, this thesis will focus on the development of mono-fuel natural gas engines and improvements in injection and combustion strategies have to be reached by implementing new combustion chamber shape, improved ignition management and improved injection systems. A detailed analysis of the natural gas injection system will be hence carried out. Different injection system layouts will be analyzed: single-point, multi-point and direct injection systems, focusing on pressure reducing valve dynamic. As a matter of fact, its behavior affects the dynamic response of the injection system: mismatch between estimated injected fuel and real one could be appreciated. Typically, average rail pressure evaluated by ECU differs from mean value during injection window. Therefore, detailed analysis will be carried out on experimental data and a 0D-1D numerical model will be v developed to enhance the problem understanding. The research activity has been carried out in order to reproduce properly all the components of the pressure reducing valve which affects the dynamic response of the injections system. The numerical model will give useful explanation of the fuel mass injected mismatch. Then, a heavy-duty spark ignition compressed natural gas engine provided with two different injection systems will be examined. A standardized single-point injection system and a prototypal multi-point one will be evaluated so as to evaluate the possibility for performance enhancement. Cyclic variation and combustion efficiency for each configuration will be analyzed, proving the highest combustion efficiency of the prototypal configuration. Moreover, possible improvements with new engine control strategies will be investigated by adopting a 0D-1D numerical model. Single-point injection system modelling will prove the impossibility for efficiency improvement whereas multi-point injection system can be optimized by adopting enhanced strategies. As a matter of fact, fire-skipping mode will be simulated. Feasible reductions of fuel consumption under partial load conditions will be shown: decrease in fuel consumption up to 12% will be proved. Finally, a new methodology for combustion, cyclic variation and knock onset modelling will be presented. Indeed, high-efficiency natural gas engines could in turn lead to knock conditions due to higher CR and different combustion chamber shape. Experimental analysis at test bench could be carried out to calibrate appropriate ECU control strategies for knock mitigation, but an experimental campaign under knock condition is dangerous and costly due to possible failure of mechanical parts of the engine. Numerical models for auto-ignition prediction could hence overcome this problem. Therefore, a predictive fractal combustion tool will be calibrated: it will be able to perform a correct mass fraction burned evolution estimation for different operating conditions (speeds, loads, relative air-to-fuel ratio, etc.). Then, knock onset estimation based on auto-integral (its usage is satisfactory considering the high natural gas chemical stability) coupled with a new method for cyclic variability simulation will be adopted; these two phenomena are indeed strictly correlated. A correct estimation of the percentage of knocking cycles will be shown. This new methodology will be carried out and verified on two light-duty spark ignition engines with different characteristics so as to verify its goodness