To improve the performance of particle image velocimetry in measuring instantaneous velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.

Theory of cross-correlation analysis of PIV images : Image analysis as measuring technique in flows

https://www.ourenergypolicy.org/wp-content/uploads/2011/12/2010_03_Elsevier_InterJourHydrogenEnergy_Balat_HydrogenFromBiomass.pdf

Hydrogen from biomass – Present scenario and future prospects

Spark ignition natural gas engines—A review

Petroleum resources are finite and, therefore, search for their alternative non-petroleum fuels for internal combustion engines is continuing all over the world. Moreover gases emitted by petroleum fuel driven vehicles have an adverse effect on the environment and human health. There is universal acceptance of the need to reduce such emissions. Towards this, scientists have proposed various solutions for diesel engines, one of which is the use of gaseous fuels as a supplement for liquid diesel fuel. These engines, which use conventional diesel fuel and gaseous fuel, are referred to as ‘dual-fuel engines’. Natural gas and bio-derived gas appear more attractive alternative fuels for dual-fuel engines in view of their friendly environmental nature. In the gas-fumigated dual-fuel engine, the primary fuel is mixed outside the cylinder before it is inducted into the cylinder. A pilot quantity of liquid fuel is injected towards the end of the compression stroke to initiate combustion. When considering a gaseous fuel for use in existing diesel engines, a number of issues which include, the effects of engine operating and design parameters, and type of gaseous fuel, on the performance of the dual-fuel engines, are important. This paper reviews the research on above issues carried out by various scientists in different diesel engines. This paper touches upon performance, combustion and emission characteristics of dual-fuel engines which use natural gas, biogas, producer gas, methane, liquefied petroleum gas, propane, etc. as gaseous fuel. It reveals that ‘dual-fuel concept’ is a promising technique for controlling both NOx and soot emissions even on existing diesel engine. But, HC, CO emissions and ‘bsfc’ are higher for part load gas diesel engine operations. Thermal efficiency of dual-fuel engines improve either with increased engine speed, or with advanced injection timings, or with increased amount of pilot fuel. The ignition characteristics of the gaseous fuels need more research for a long-term use in a dual-fuel engine. It is found that, the selection of engine operating and design parameters play a vital role in minimizing the performance divergences between an existing diesel engine and a ‘gas diesel engine’.

Effect of engine parameters and type of gaseous fuel on the performance of dual-fuel gas diesel engines—A critical review

Knocking combustion in spark-ignition engines

A partially stratified charge (PSC) engine concept has been developed to improve the combustion process in a spark ignition engine fuelled by natural gas, operating at lean air-fuel ratios. In general, this technique is effective at increasing fuel conversion efficiency and brake mean effective pressure at relative air-fuel ratios greater than lambda = 1.5. Preliminary testing at 2500 r/min showed that PSC reduced combustion duration by almost 10 per cent at a given air-fuel ratio. It was also effective in extending the lean limit of engine operation, which meant that the engine could be run at lower loads without throttling. PSC technology provides an alternative method of load control to throttling, and hence reduces associated pumping losses. Further investigation was conducted at 1500 r/min and a lean air-fuel ratio of lambda = 1.65. PSC was found to significantly improve engine performance when compared with homogeneous charge operation at the same air-fuel ratio. The optimized data were compared to simple throttled and lean baseline data and a dramatic reduction in NOx emissions was observed, with little efficiency penalty. These initial results demonstrate that the leanburn, partially stratified charge strategy is a viable means of engine control, and has significant performance and emissions benefits.

Improving emissions and performance characteristics of lean burn natural gas engines through partial stratification

One of the most important issues facing humanity today is the prospect of global climate change, brought about primarily by our prolific energy use and heavy dependence on fossil fuels. Fueling Our Future: An Introduction to Sustainable Energy provides a concise overview of current energy demand and supply patterns. It presents a balanced view of how our reliance on fossil fuels can be changed over time so that we have a much more sustainable energy system in the near future. Written in a non-technical and accessible style, the book will appeal to a wide range of readers without scientific backgrounds.

Fueling Our Future: An Introduction to Sustainable Energy

A cylinder head, more preferably a piston, of an internal combustion engine is provided on its compression face with a substantially central bowl and a plurality of discrete squish jet channels circumferentially spaced about the bowl. Each of the channels is open to the compression face along its full length from an inlet end to a discharge end opening into the bowl. The channels provide the main paths for fluid flow from the areas on compression face surrounding the bowl into the bowl. The piston and cylinder are so shaped that as the piston approaches top dead center position the air fuel mixture is forced from the compression face into and along the channels from the inlet end to the discharge end and are discharged as interacting jets into the bowl and increase the turbulence in the air fuel mixture in the bowl.

Squish jet combustion chamber

A squish jet arrangement for an internal combustion engine is positioned on a piston member or cylinder head member thereof. A substantially cylindrical bowl opens onto the face of the member. At least one pair, and preferably a plurality of pairs, of squish jet passages are arranged to direct flows of gasses tangentially into the bowl. As first ones of the pairs of squish jet passages lie in a lower transverse plane than second ones of the pairs, a counter-rotating, bi-level swirl can be produced by the squish jet outlets. A squish jet arrangement is also provided with outlets of squish jet passages spaced above a lower surface of a bowl, and directed to eject coplanar flows of gasses therefrom, which intercept one another.

Internal combustion engine squish jet combustion chamber

A series of tests was conducted on a Toyota, four-cylinder, spark ignition engine which was modified to run on either gasoline or natural gas. The aim of the experiment was to investigate the performance and combustion behavior of natural gas, with particular emphasis on its low burning velocity. A pressure transducer installed in the cylinder head was used to obtain pressure versus crank angle curves from which mass burn rates and burning velocities were calculated, using a heat release analysis program. Results indicate that the low laminar burning velocity of natural gas extends its ignition delay period (time to 1 percent burned) by up to 100 percent compared with gasoline. This contrasts with the remainder of the combustion period which is dominated by turbulence effects that produce very similar burning velocities for the two fuels.

Robert L. Evans

Papers

Improving emissions and performance characteristics of lean burn natural gas engines through partial stratification

Fueling Our Future: An Introduction to Sustainable Energy

Squish jet combustion chamber

Internal combustion engine squish jet combustion chamber

Comparison of Burning Rates in a Natural-Gas-Fueled Spark Ignition Engine