Abstract. In many heat devices designers and operators meet the problem of low efficiency of combustion and restricted emission standards. This process should be improved to maximize its efficiency and satisfy additional requirements as, for example, uniform temperature fieldin combustion chamber, low noise level or very low NOx emission. These requirements are satisfied by homogeneous combustion. Such combustion method is particularly attractive for the steel or glass industry or power industry based in particular on natural gas. In this paper factors, which have the biggest influence on performance of flameless combustion, are discussed, among others: momentum of fuel and oxidizer, composition of the mixture, the temperature of the inlet gases. Additionally, blind simulations of combustion in a combustion chamber of a furnace are run to assess how high is the influence of these factors individually. Numerical simulations are performed in a CFD code AVL Fire. The detailed chemical kinetics mechanism GRI-mech 3.0 is used for combustion calculations. Calculations results are correlated with experimental data. Blind simulations and experiment provide similar level of NO X emission (~6-8 ppm). Experiments showed that the effect of the addition of ethylene to fuel on emissions of NO X , CO, THC is not significant. Similarly, numerical simulations predict that influence of ethylene is negligible. CO, THC and CO 2 were on a stable level across all cases. NO X emissions increases when mass flow of air and fuel increases due to higher heat release in the same volume, what results in higher temperature of combustion products. When temperature of fuel increases NO X level decreases.
A detonation is the strongest form of all gas explosions. The ease with which a flammable mixture can be detonated (detonability) commonly and traditionally is classified by a detonation cell width λ and an ignition delay time behind the detonation leading shock τ. Additionally, two more parameters were proposed 3 years ago -χ and RSB, which inform about regularity of a detonation structure. The problem of a detonation is significant in industry, in particular in power engineering, where restricted emission standard impose to introduce hydrogen-rich fuels, such as syngas. The most possible initiation of a detonation in industrial conditions is deflagration to detonation transition (DDT), where a deflagration under some conditions (obstacles, confinement, etc.) accelerates and a transition to a detonation takes places. In industry, this acceleration of a flame may progress in initially smoke-filled space. The goal of this paper is to analyse influence of exhaust gas on detonation propensity of a mixture of carbon monoxide and hydrogen. The analysis concerns the detonation cell width λ, ignition delay time τ, RSB and χ parameters. The composition of exhaust gas is calculated by setting it to a state of chemical equilibrium. Combustion temperature influence on exhaust gas composition is assessed. Species, which have the strongest influence on detonability, are assessed. Computations are performed with the use of Cantera tool.
The aim of this study was to investigate a possibility of using gaseous fuels of a low calorific value as a fuel for internal combustion engines. Such fuels can come from organic matter decomposition (biogas), oil production (flare gas) or gasification of materials containing carbon (syngas). The utilization of syngas in the barrel type Opposed-Piston (OP) engine arrangement is of particular interest for the authors. A robust design, high mechanical efficiency and relatively easy incorporation of Variable Compression Ratio (VCR) makes the OP engine an ideal candidate for running on a low calorific fuel of various compostion. Furthermore, the possibility of online compression ratio adjustment allows for engine the operation in Controlled Auto-Ignition (CAI) mode for high efficiency and low emission. In order to investigate engine operation on low calorific gaseous fuel authors performed 3D CFD numerical simulations of scavenging and combustion processes in the 2-stroke barrel type Opposed-Piston engine with use of the AVL Fire solver. Firstly, engine operation on natural gas with ignition from diesel pilot was analysed as a reference. Then, combustion of syngas in two different modes was investigated – with ignition from diesel pilot and with Controlled Auto-Ignition. Final engine operating points were specified and corresponding emissions were calculated and compared. Results suggest that engine operation on syngas might be limited due to misfire of diesel pilot or excessive heat releas which might lead to knock. A solution proposed by authors for syngas is CAI combustion which can be controlled with application of VCR and with adjustment of air excess ratio. Based on preformed simulations it was shown that low calorific syngas can be used as a fuel for power generation in the Opposed-Piston engine which is currently under development at Warsaw University of Technology.
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