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Non-crossing Rectilinear Shortest Minimum Bend Paths in the Presence of Rectilinear Obstacles

Nagaraja S.

Journal of Telecommunications and Information Technology

2018

nr 3

82--91

The paper presents a new algorithm to determine the shortest, non-crossing, rectilinear paths in a twodimensional grid graph. The shortest paths are determined in a manner ensuring that they do not cross each other and bypass any obstacles present. Such shortest paths are applied in robotic chip design, suburban railway track layouts, routing traffic in wireless sensor networks, printed circuit board design routing, etc. When more than one equal length noncrossing path is present between the source and the destination, the proposed algorithm selects the path which has the least number of corners (bends) along the path. This feature makes the path more suitable for moving objects, such as unmanned vehicles. In the author’s scheme presented herein, the grid points are the vertices of the graph and the lines joining the grid points are the edges of the graph. The obstacles are represented by their boundary grid points. Once the graph is ready, an adjacency matrix is generated and the Floyd-Warshall all-pairs shortest path algorithm is used iteratively to identify the non-crossing shortest paths. To get the minimum number of bends in a path, we make a modiﬁcation to the Floyd-Warshall algorithm, which is constitutes the main contribution of the author presented herein.

Experimental study on performance and emission characteristics of lean burn SI engine fuelled with hydrogen methane blends

Przybyła G., Nagaraja S.

Combustion Engines

2015

R. 54, nr 3

556--562

An experimental study on the performance and exhaust emissions of a spark ignition engine fueled with methane(CH4)-hydrogen (H2) blends was carried out at a constant speed of 1500 rpm and fixed excess air ratio (λ) of 1.5. The tests were carried out for pure methane and 2 blends (93% (by vol.) CH4 + 7% (by vol.) of H2, 77% (by vol.) CH4 + 23% (by vol.) of H2) at part load conditions in a naturally aspirated, three cylinder engine with a compression ratio of 9.3:1. The effects of hydrogen addition was studied at various spark timing and it is observed that the Maximum Brake Torque timing (MBT) retarded with increase in concentration of hydrogen. The coefficient of variation in indicated mean effective pressure (COVimep) decreases in blends, indicating stable combustion with hydrogen enrichment. A decrease in burn duration is observed and the crank angle at which peak pressure occurred, is tending towards top dead center (TDC) with increase in concentration of hydrogen due to higher laminar flame speed of the mixture enriched with hydrogen. In case of blends, specific emissions of carbon monoxide (CO) and unburned hydrocarbons (HC) decreases. However, there is considerable increase in specific emissions of oxides of nitrogen (NOx).

Przeprowadzono badania eksperymentalne energetycznych parametrów pracy silnika spalinowego ZI oraz jego oddziaływania na środowisko naturalne podczas zasilania mieszaniną metanu z wodorem. Analizowano pracę silnika podczas spalania mieszanki ubogiej (λ = 1,5) przy stałej prędkości obrotowej wynoszącej 1500 obr/min. Badania wykonano dla zasilania czystym metanem oraz dwiema mieszankami o różnym udziale objętościowym wodoru tj. 7% H2, 93% CH4 oraz 23% H2, 77% CH4. Badano wpływ kąta wyprzedzenia zapłonu na przebieg procesu spalania. Zaobserwowano, że optymalna wartość kąta wyprzedzenia zapłonu zmniejsza się dla wyższej zawartości wodoru w mieszance palnej. Ponadto wskaźnik sygnalizujący poziom niepowtarzalności pracy indykowanej w kolejnych cyklach roboczych osiąga niższe wartości dla mieszanek wzbogaconych wodorem, co oznacza stabilniejszy przebieg procesu spalania. Spalanie mieszanek metanu z wodorem prowadzi do nieznacznego ograniczenia emisji CO oraz HC, natomiast wielkość emisji NOx rośnie za sprawą wyższej temperatury spalania dla mieszanki CH4 , H2.