An Experimental Investigation of the Burn Rates of Naturally Aspirated Spark Assisted Compression Ignition Combustion in a Single Cylinder Engine with Negative Valve Overlap.

The implementation of homogeneous charge compression ignition (HCCI) in an engine remains a challenge due to the limited operating range and lack of a direct ignition timing control mechanism. Spark assisted compression ignition (SACI) has been shown by several research groups, including the work presented here, to provide such a mechanism, helping to control the phasing and stability of a primarily auto-igniting charge, as well as provide a means of extending the high load limit of HCCI while maintaining high thermal efficiency. The approach used in this study is unique in that flexible engine valve timing allowed for independent control of the thermal/compositional stratification associated with a large internal residual fraction, allowing its effect to be isolated from other thermophysical parameters. In these experiments, a single-cylinder engine equipped with fully-flexible valve actuation was used to explore the effects of spark assist in controlling peak heat release rates. With spark assist, a small portion of the heat release occurred via flame propagation, increasing the overall duration of the combustion event and dramatically reducing peak rates of heat release. At constant engine load and combustion phasing, peak heat release rates were reduced by 40% by controlling spark timing and unburned gas temperature via changes in internal and external EGR rates. Internal EGR was adjusted by varying the duration of negative valve overlap (NVO); for the range of NVO investigated, potential variations in in-cylinder mixing and thermal/compositional stratification were found to have a weak effect on burn characteristics, confirming the notion that temperature and spark timing are the primary variables affecting SACI burn rates for a fixed mixture composition. In the experiments, heat release analysis showed that the behavior of SACI was consistent with the theoretical kinetics associated with turbulent flame propagation and auto-ignition, supporting the hypothesis that SACI is essentially two distinct energy release events coupled by compression heating from an expanding flame front. The results of this work provide new insights into the physical and chemical mechanisms important during low temperature combustion. The results confirm proposed representations of SACI, and thereby provide direction for developing new advanced low temperature engine strategies.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/99979/1/manofsky_1.pd

The control of an unthrottled homogeneous DISI engine through reduced intake valve lift and duration : a study of the in-cylinder flows and charge formation

This research investigated a novel combustion system for gasoline direct injection spark ignition (DISI) engines. This combustion system burned an unthrottled, stoichiometric, homogenous charge at part load, in comparison to the unthrottled,lean, stratified charge burned by conventional DISI engines. Unthrottled homogeneous operation, enabled by the use of variable valve timing. allowed high fuel efficiencies to be achieved while addressing the particulate emissions, poor combustion stabilities and NOx after-treatment issues associated with stratified charge DISI engines, when compared to the port fuel injection (PFI) engines they are replacing. Experiments were performed to quantifY the bulk in-cylinder air motions, determine their effect on the fuel spray, and examine the resulting air-fuel mixture preparation of various early inlet valve closing (EIVC) and late inlet valve opening (LIVO) strategies that were suitable for controlling engine load under homogeneous engine conditions. A broad matrix of engine conditions has been investigated, with engine speeds ranging from idle (750 rpm) to 5000 rpm, and engine loads ranging from 2.7 bar indicated mean effective pressure (!MEP) to wide open throttle (WOT). Particle Image Velocimetry (PIV) was used to record mean in-cylinder flow fields in the tumble and swirl planes for a range of engine conditions and valve profiles. This included measurements at higher engine speeds (3500rpm) than previously published. Air flows in the difficult-to-access cylinder head were measured with Laser Doppler Anemometry (LDA) and the effect of these air flows on the fuel spray produced by a latest generation multi-stream fuel injector was investigated with Mie imaging. The resulting mixture preparation was then investigated over a crank angle period ranging from the start ofinjection (SOl) to the time of spark with Laser Induced Exciplex Fluorescence (LIE F). Supporting data from a thermodynamic sister engine with identical combustion chamber geometry was recorded at University College London. Unthrottled, homogeneous operation with low lift EIVC valve profiles improved engine fuel consumption by up to 20% compared to throttled operation with conventional, full-lift profiles. This was a consequence of a reduction in the throttling losses and improvements in air-fuel mixing. The intake air momentum was more significant than the fuel spray momentum from the injection system in determining the air-fuel mixing process. This resulted in engine performance being strongly affected by engine speed, intake valve lift and injection timing. The greatest benefits in ISFC occurred when only one of the two inlet valves was operated. This was attributed to an overall increase in the level ofin-cylinder swirl. However, the choice of which inlet valve was opened was critical, with greater gains occurring if the fuel spray from the centrally mounted injector was directed towards the spark plug than when the spray was directed away from the plug. EIVC combustion also exhibited significantly longer burn times than throttled operation. This was due to lower cylinder pressures that reduced the laminar flame speed and lower levels of turbulence around the spark plug at the time of ignition. Flame front measurements on the optical engine showed that during the longer early heat release phase (0-10% mass fraction burned), the flame kernel was transported away from the spark plug and towards the combustion chamber wall beneath the inlet valves. Investigations into the fuel mixture preparation using Laser Induced Exciplex Fluorescence (LIE F) demonstrated that, under high load conditions, a source of particulate emissions from PFI engines was large droplets in the vicinity of the spark plug around the time of ignition. These fuel rich regions were precursors in the generation of soot and were all but eliminated with direct injection fuelling strategies. Late Intake Valve Opening (LIVO) valve strategies generated a sub-atmospheric cylinder pressure of between 0.5 to 0.3bar (absolute). Spray images obtained under these conditions showed greater penetration of the fuel spray and a poorly defined spray cone boundary. Due to the increased momentum and increased shear forces of the inducted air, and the cylinder pressure falling below the saturation vapour pressure of some components of the gasoline fuel at the temperature of the mixture, flash evaporation of those components was seen to occur. The improvement in atomisation and faster burn rate with LIVO compensated to some extent for the increase in irrecoverable pumping work of this operating strategy over conventional EIVC. However, a practical disadvantage of LIVO was poor control of the trapped air mass, arising from the intake air momentum supercharging the engine cylinder at the conditions tested.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Intelligent techniques for improved engine fuel economy

ii This thesis presents an investigation into a novel method of estimating the trajectory (future direction and elevation) of a vehicle, and subsequently influencing the control of an engine. The technique represents a convenient and robust method of achieving road prediction, to form a fuzzy system that „looks ahead‟, leading potentially to improved fuel consumption and a consequent reduction in exhaust emissions. The work described in this thesis brings together two modern technologies, Neuro-fuzzy techniques and Global Positioning System, and applies them to engine/vehicle control. The intelligent GPS-based control system presented in this thesis utilises information about the current vehicle position and upcoming terrain in order to reduce vehicle fuel consumption as well as improve road safety and comfort. The development of such in-vehicle control systems has provided static and dynamic road information. The vehicle running parameters have been mathematically defined whilst the engin

Experimental Investigation And Development Of An Extended Two Color Method (etcm) With Application To Internal Combustion Engines

The internal combustion engine is on a continuous path of improvement to reduce exhaust gaseous emissions and improve fuel economy. While recent trends in diesel engine development have lowered the EGR requirements, future regulatory pressure will likely result in a reversed trend in the future. Given this, it is of interest to improve the application range of diagnostic tools such as the two color method (TCM) typically used in evaluating the properties of engine soot, such as temperature and volume fraction. This optical diagnostic method relies on the use of the light emitted by the soot particles along with a soot emissivity model in order to estimate the temperature T and optical thickness KL characterizing the soot cloud of interest. This assumption is reasonable for the traditional diesel combustion, where low degrees of premixed combustion result in very low amounts of blue-flame light emission compared to the soot related radiation. However, for LTC (low temperature combustion) combustion modes this assumption is no longer applicable, especially for combustion strategies characterized by very large premixed combustion phases, such as the Partially-premixed Charge Compression Ignition (PCCI) strategies. The aim is to obtain more information related to the combustion process and specifically on the soot formation and oxidation process. For this reason, the present research can be divided in two major sections. The first section focuses on the development of a combustion optical probe and the optical experimental setup necessary for conducting the experimental work. Information regarding the soot formation and oxidation processes may be inferred from the measured signal. The objective of the second section of the current research is to provide the theoretical background and experimental evidence needed to describe the proposed optical diagnostic tool, the extended two-color method (eTCM). This method attempts to extend the domain of applicability of the classical two color method within the area of strong CO continuum interference as well as providing a method of testing the validity of the conventional two-color method. Further, it provides additional information regarding the strength of the radiation associated with the CO flame continuum. Towards this goal, the work was conducted on a fully accessible optical engine, which allowed the use of multiple synchronous optical measurements targeted towards the evaluation of the proposed optical diagnostic tool. The evidence presented in this work suggests that eTCM is capable of temperature and soot optical thickness factor correction under medium and strong blue-flame interference without significant impact on the temperature estimation uncertainty. Consequently, the currently proposed extended two-color method (eTCM) has the potential for a large-scale impact in the fields of fundamental engine research as well as engine development and calibration

Thermal Emission of Strontium Products for Scalar Diagnostics in Internal Combustion Engines

Developments in optical diagnostics for combustion systems have been essential to the recent improvements in efficiency and abatement of emissions that internal combustion engines have undergone recently. Great emphasis has been placed in the measurement of quantities with high temporal and spatial resolution, which has enabled the understanding of key physical and chemical processes, but there remains a need for obtaining spatially integrated measurements to understand how local events affect the overall behavior of the gases in a turbulent combustion chamber. Strontium offers a potential avenue to provide these measurements. When present in combustion it produces strontium monohydroxide, which spontaneously emits radiation in several bands of the visible spectrum, and thus enables the determination of temperature independently of species concentration through the Boltzmann distribution. Further, chemical equilibrium calculations can relate equivalence ratio to the relative concentration strontium and strontium monohydroxide, which could also be measured optically. The potential of this technique was explored in this work. An optical engine was operated under different conditions with a strontium-containing fuel and spectral measurements of the radiation emitted from the chamber were performed. The temperature in the cylinder was predicted by a one-dimensional thermodynamic model that used a two-zone model for flame propagation. The relative spectrally resolved emission intensity of atomic strontium and strontium monohydroxide was measured using a spectrometer coupled with camera, and the collected signals were related to the conditions in the chamber. From the results the mathematical formulation for the relationship of spectral intensity with temperature was found to be adequate, and important insights for the application of the diagnostic in imaging experiments were obtained. A universally applicable calibration was not attained due to experimental limitations, however, but the key barriers to overcome were identified.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/153368/1/ivantib_1.pd

Mechanical Engineering

The book substantially offers the latest progresses about the important topics of the "Mechanical Engineering" to readers. It includes twenty-eight excellent studies prepared using state-of-art methodologies by professional researchers from different countries. The sections in the book comprise of the following titles: power transmission system, manufacturing processes and system analysis, thermo-fluid systems, simulations and computer applications, and new approaches in mechanical engineering education and organization systems

Active control of spray combustion

Effect of a forced dilution air jet on air-fuel spray mixing and emissions has been investigated. Temperature measurements have been made at a number of forcing frequencies in the range of 100-1100 Hz and blowing ratios between 6-15. Open-loop flame response to forcing has also been acquired by recording pressure and heat release spectra. The results show that the mean temperature field inside the flame can be altered due to jet modulation. Significant effects are observed by forcing at locations close to the dump plane. Enhancements in temperature of the order of 100–200 ˚C, and reduction in pattern factor of the order of 40% were observed. Substantial reductions in nitric oxide emissions can be obtained over a range of flow conditions. More rigorous burning can be obtained due to enhanced fuel air mixing. A multi-resolution technique is utilized to analyze temperature fields to decompose the response of different hierarchical scales to forcing. Forcing is found to have most impact on large-scale structures that are in the order of characteristic jet length scale. Bulk mixing is not the only factor that determines pollutant emissions level. Consequently, there exist select frequencies, which affect both emissions and mixing positively. An artificial intelligence based extremum-seeking algorithm is introduced to optimize the combustor behavior. The second part of this dissertation deals with syngas combustion. Stability of a pre-mixed gas turbine combustor is quite sensitive to fuel composition. Behavior of a premixed confined hydrogen enriched methane flame is studied with regard to thermo-acoustic instability induced flashback, emissions, flammability limits and acoustics over a range of conditions. Hydrogen addition extends the flammability limits and enables lower emissions levels to be achieved. Contrarily, increased RMS pressure fluctuation levels, and higher susceptibility to flashback is observed with increasing hydrogen volume fraction inside the fuel mixture. In addition, a semi-analytical model has been utilized to capture the flame holding and flashback dynamics utilizing G-equation. A limit cycle behavior in the flame front movement is observed due to a non-linearity in the feedback term. Experiments including phase locked radical imaging and PLIF measurements have been performed at varying fuel composition

Bibliography of Lewis Research Center technical publications announced in 1987

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1987. All the publications were announced in the 1987 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses