Effect of spark ignition location on the turbulent jet ignition characteristics in a lean burning natural gas engine

The Turbulent Jet Ignition is an effective concept to achieve stable lean burning for natural gas engines due to the multiple ignition sources, high ignition energy, and fast combustion rate. A variation of the ignition location has a non-negligible effect on the ignition performance of the TJI system. The present work aims to provide more details on this effect by numerical simulations. Both factors of the additional fuel supply to the pre-chamber and the in-cylinder flow field are taken into consideration in this study. A numerical model is built based on a lean burning natural gas engine and validated by experimental results. Five different spark ignition sources are equally arranged on the vertical axis of the pre-chamber, with different distances from the connecting orifices. Simulations are carried out under the same initial and boundary conditions except for the location of the ignition source. Combustion pressure, in-cylinder flow field, fuel mass fraction distribution, and heat release rate are analyzed to study the in-cylinder ignition and combustion process. The results show that a rotational flow and a non-uniform fuel distribution are formed in the pre-chamber during the compression stroke. The turbulent jet characteristics are significantly influenced by the coupling of two factors: the combustion rate inside the pre-chamber as well as the flame propagation distance from the ignition source to the connecting orifices. Rapid combustion rate and shorter flame propagation distance both lead to the earlier ejection of cold jets and hot jets. Among five ignition sources, the one located closest to the connecting orifices generates earlier hot jets with the highest mean velocity. The jets are more effective to ignite the lean mixture and could decrease the combustion duration of the main chamber.

Скорость горения порошкообразного пористого кремния в условиях ограниченного пространства

The method of determination combustion rate of powdered porous silicon with limited space is presented. The values of the combustion rates of porous silicon are close to the values of the rates of explosives.

UJI MUTU BRIKET DARI PENCAMPURAN JERAMI DAN SEKAM PADI DARI LIMBAH PASCA PANEN DI LAHAN GAMBUT

This study aims to conduct a study of the quality value of briquettes made from mixing straw and rice husks which include a flame test and combustion rate which is expected to be used to educate people around the forest by providing innovation and technology regarding the use of post-harvest waste. The results showed that the value of the quality of briquettes made from variations in the mixing of straw and rice husks including the flame test of the combustion rate obtained results, for treatment A (100% straw) of 0.68 gr/minute, treatment B (100% husk) of 0 ,57 gr/minute, treatment C (Husk 75% + Straw 25%) was 0.40 gr/minute, treatment D (Husk 25% + Straw 75%) was 0.46 r/minute and treatment E (Husk 50% + Straw 50%) of 0.43 gr/minute. The value of the flame to boiling time for treatment A = 38.62 minutes, treatment B = 31.05, treatment C = 23.22 minutes, treatment D = 36.05 and treatment E = 27.95 minutes. Density values of all treatments, and the water content for treatment B and treatment C can meet SII. While other parameters: ash content, volatile matter, bound carbon and calorific value still cannot meet the standards, so it is recommended to carry out further research with other variations of treatment, in order to obtain briquettes with quality that can meet the standards.

ANALISIS NILAI KALOR DAN LAJU PEMBAKARAN BRIKET TONGKOL JAGUNG SEBAGAI SUMBER ENERGI ALTERNATIF

ABSTRAKTujuan dari penelitian ini yaitu untuk menghasilkan briket tongkol jagung sebagai alternative sumber energi yang memiliki nilai kalor yang tinggi. Briket tongkol jagung dibuat dari tongkol jagung yang sudah dikeringkan dan dihaluskan sebelumnya dengan ukuran 20 mesh. Masing-masing perlakuan dicetak dengan variasi persentase perekat tepung tapioka yaitu 5%, 10%, dan 15%. Selain variasi perekat dilakukan juga variasi tekanan pembentukannya untuk melihat komposisi terbaik yang menghasilkan nilai kalor yang tinggi dan laju pembakaran yang sesuai. Briket selanjutnya diuji nilai kalor dan laju pembakarannya dengan menggunakan alat bom calorimeter. Hasil penelitian menunjukkan bahwa secara berturut-turut nilai kalor dan laju pembakaran briket dengan persentase komposisi perekat 5%, 10%, 15% yaitu 21,00 kJ, 22,68 kJ, 31,08 kJ, dan 12,00 gram/menit, 13,33 gram/menit, 13,50 gram/menit. Hasil terbaik dihasilkan pada komposisi persentase perekat 15% dengan nilai kalor mencapai 31,08 kJ, dan laju pembakaran 13,50 gram/menit yang tidak terlalu jauh meningkat dibandingkan dengan komposisi persentase perekat lainnya. Kata kunci: briket; tongkol jagung; nilai kalor; laju pembakaran ABSTRACTThe purpose of this research is to produce corn cobs briquettes as an alternative energy source that has a high calorific value. Corn cobs briquettes are made from corn cobs that have been dried and previously mashed with a size of 20 mesh. Each treatment was printed with variations in the percentage of tapioca starch adhesive, namely 5%, 10%, and 15%. In addition to variations of the adhesive, variations in the formation pressure were also carried out to see the best composition that produced a high heating value and an appropriate combustion rate. The briquettes were then tested for calorific value and rate of combustion using a bomb calorimeter. The results showed that the calorific value and burning rate of briquettes with the percentage of adhesive composition 5%, 10%, 15%, were 21.00 kJ, 22.68 kJ, 31.08 kJ, and 12.00 gram/minute, respectively. 13.33 grams/minute, 13.50 grams/minute. The best results were obtained at 15% adhesive percentage composition with a calorific value of 31.08 kJ, and a burning rate of 13.50 gram/minute which was not significantly increased compared to other adhesive percentage compositions. Keywords: briquettes; corn cobs; calorific value; combustion rate

Numerical determination of the combustion rate of a gas suspension of coal dust in a propane-air mixture

The results of the numerical solution of the problem of the combustion rate of a coal-propane-air mixture are presented. The physical and mathematical formulation of the problem is based on the approaches of the dynamics of multiphase reacting media. The method for solving the problem is based on the algorithm for the decay of an arbitrary discontinuity. The dependences of the visible and normal combustion rate of the coal-propane-air mixture on the radius and the volumetric content of propane in the gas are obtained.

Karakteristik Briket Biomassa dari Variasi Bahan Baku dan Persentase Perekat yang Berbeda

ABSTRAK Penelitian ini bertujuan untuk menganalisa karakteristik dan pengaruh jenis bahan baku dan persentase perekat yang berbeda terhadap mutu briket biomassa yang dihasilkan dan menentukan perlakuan manakah yang memberikan hasil terbaik terhadap karakteristik briket yang dihasilkan. Penelitian ini menggunakan Rancangan Acak Kelompok (RAK) Faktorial dengan menggunakan 2 faktor dan 3 kali ulangan. Faktor pertama (A) adalah jenis bahan baku yang terdiri dari 3 taraf yaitu bambu tabah ( A1), sekam padi (A2) dan campuran bambu tabah dan sekam padi (A3). Faktor kedua (B) adalah persentase perekat yang terdiri dari 3 taraf yatu konsentrasi 10%, ( B1) 15% (B2) dan 20%(B3) . Parameter penelitian yang diamati adalah kadar air, kadar abu, kadar zat menguap dan laju pembakaran. Seluruh perlakuan diulang sebanyak 3 kali ulangan sehingga didapatkan 27 unit percobaan. Data yang diperoleh dianalisis dengan sidik ragam dan apabila terdapat pengaruh perlakuan yang signifikan, maka dilanjutkan dengan uji Duncan Multiple Test (DMRT). Berdasarakan hasil penelitian diketahui bahwa, interaksi perlakuan memberikan pengaruh yang signifikan terhadap parameter kadar air, kadar abu, kadar zat menguap dan laju pembakaran. Selanjutnya Kadar air yang didapat berkisar antar 2,30% bb - 4,78%,bb kadar abu 5,88% - 34,85%, kadar zat menguap 31,30% - 51,59% dan laju pembakaran 73,20 gr/menit – 106,00 gr/menit. Kualitas briket yang paling baik diperoleh pada perlakuan A2B3 (sekam 80 gram perekat 20 gram) dimana kadar air yang dihasilkan sebesar 2,30%bb, kadar abu 32,29%, kadar zat menguap 32,01% dan laju pembakarannya selama 92,60 gr/menit. ABSTRACT This study aims to analyze the characteristics and effects of different types of raw materials and adhesive percentages on the quality of the briquettes of the biomass produced and to determine which treatment gives the best results for the characteristics of the resulting briquettes. This study used a factorial randomized block design (RBD) using 2 factors and 3 replications. The first factor (A) is the type of raw material which consists of 3 levels, namely tabah bamboo (A1), rice husk (A2) and a mixture of tabah bamboo and rice husk (A3). The second factor (B) is the adhesive percentage consisting of 3 levels, namely 10% concentration, (B1) 15% (B2) and 20% (B3). The research parameters observed were moisture content, ash content, volatile substance content and combustion rate. All treatments were repeated 3 times in order to obtain 27 experimental units. The data obtained were analyzed using variance and if there was a significant treatment effect, it was followed by the Duncan Multiple Test (DMRT). Based on the results of the study, it is known that the treatment interaction has a significant effect on the parameters of moisture content, ash content, volatile substance content and combustion rate, then the moisture content obtained ranges from 2.30% bb - 4.78%, bb ash content 5, 88% - 34.85%, the volatile substance content was 31.30% - 51.59% and the combustion rate was 73.20 grams/minutes - 106.00 grams/minutes. The best quality of briquettes was obtained in A2B3 treatment (80 grams of rice husk 20 grams of adhesive) where the water content produced was 2.30%, the ash content was 32.29%, the vaporizing substance content was 32.01% and the burning rate was 92.60 grams. /minute.

Numerical Simulation of Interaction between Large-Scale Congestion and Vent during the Natural Gas Explosion in a Kitchen

The influence of large-scale congestion on a confined natural gas explosion in a typical Chinese kitchen was studied using the computational fluid dynamics technology. It was found that opening the explosion venting surface promotes the development of turbulence, flame propagation velocity, and multipeak overpressure in the explosion flow field. Large-scale congestion can significantly strengthen the influence of the explosion venting surface on the flow field; the congestion and the explosion venting surface have a synergistic effect on the explosion flow field. At the moment of gas explosion, the flow fields in each area of the kitchen exhibit different distribution characteristics. A flow field near small-scale congestion is more likely to produce greater turbulence, combustion rate, and flame speed. The obstruction effect of large-scale congestion perpendicular to the flame propagation direction is dominant. The indoor flame propagation speed and overpressure development speed increase and the peak combustion rate and indoor peak overpressure decrease with an increase in obstacle blockage. Increases in the large-scale volume congestion rate and volume blockage in the kitchen induce changes in the indoor flame propagation mode and increase the external explosion overpressure. This paper investigated the correlation behavior between large-scale congestion and vent surface in a typical Chinese civil kitchen during natural gas explosion process and provided important support for understanding the mechanism of congestion on gas explosion process and the distribution of explosion hazards in a kitchen.

Reactive Ni–Al-Based Materials: Strength and Combustion Behavior

The effect of PTFE, continuous boron, and tungsten fibers on the combustion behavior and strength of reactive Ni–Al compacts was examined in this study. The introduction of continuous fibers into Ni–Al compacts according to the developed scheme was found to increase the flexural strength from 12 to 120 MPa. Heat treatment (HT), leading to chemical interaction of the starting components, increases the strength of compacts at temperatures not exceeding 550 °C. The combination of reinforcement and HT significantly increases the strength without reducing reactivity. Experimental results showed that strength and combustion rate increase with the reduction in PTFE to 1 wt % in Ni–Al compacts. A favorable effect of the addition of PTFE from 5 to 10 wt % on the reduction of the threshold for the shock-wave initiation of reactions in Ni–Al was established. The obtained results can be used to produce reactive materials with high mechanical and energy characteristics.