Equivalence Ratio Control Research Articles

A comparison of carbon monoxide yields and particle formation at various global equivalence ratios in vitiated and under-ventilated conditions

There have been previous studies comparing experimental methods for the purpose of capturing gaseous yields at a range of global equivalence ratios. However, no work has investigated the capability of the open controlled atmosphere cone calorimeter for collecting such data where its two modes of operation are directly compared. The aim of this study is to compare carbon monoxide yields collected using vitiated and under-ventilated modes of atmospheric control in order to identify the preferable method of replicating carbon monoxide yields reported from larger scale enclosure fire experiments. Cone irradiances of 30, 50 and 65 kW/m2 were applied to PMMA and plywood samples. Vitiated tests were conducted using a mixed air/diluent gas, with an inflow rate of either 100, 150 or 180 L/min, resulting in a reduced oxygen concentration of 17.5 vol. %. Under-ventilated tests were conducted using flow rates of 5, 10 and 20 L/min in an air atmosphere. Particle formations and emissions were also measured using a particle analyser and have been reported herein. Results indicate that the under-ventilated mode of equivalence ratio control offers a more promising method of capturing species yields with favourable comparisons to other bench scale methods.

Predictive thermodynamic model of the performance of a stationary spark-ignition engine running on natural gas

In order to reduce the emissions of polluting gases and contribute to the efficient use of energy, natural gas has gained relevance due to its cleaner burning when compared to gasoline and diesel oil. In this work, a zero-dimensional thermodynamic model was developed to predict the performance, for the entire operating conditions, of a 11.7-L, six-cylinder, turbocharged spark-ignition engine used as genset and running on natural gas. This zero-dimensional model covers the closed period of the engine operating cycle. Firstly, this engine was tested in seven (7) different operating conditions to obtain the mass fraction burned and the pressure curves inside the cylinder. The combustion process was modeled using the simple Wiebe function, whose parameters were obtained from the seven (7) curves of the mass fraction burned through the Levenberg–Marquardt optimization method. Correlations were developed to estimate the Wiebe function parameters, as a function of pressure and temperature in the intake manifold, cylinder wall temperature, power and fuel consumption, for the entire operating range. The combustion efficiencies were estimated from the seven (7) experimental pressure curves with the aforementioned optimization technique. Results showed that the differences between the Wiebe function parameters obtained with the developed correlation, for the whole engine operating range, were less than 3% when compared with the Wiebe function parameters estimated for each of the seven (7) operating conditions tested. Results also showed that the thermodynamic model can be used to simulate the engine’s performance, leading to errors less than 5% when compared with the measured maximum pressure and indicated mean pressure. In addition, it was found that the delay and duration of the combustion are smaller than those usually found in spark-ignition engines and that the energy release is deficient, resulting in high specific fuel consumption. This issue can be addressed by installing an equivalence ratio control system, especially in loads above 50%, thus ensuring greater control of emissions and increasing energy efficiency.

Fuel-to-air ratio control under short-circuit conditions through UEGO sensor signal analysis

The impact of short-circuit pulses on the after-treatment system of a spark-ignited engine must be taken into account to keep the fuel-to-air equivalence ratio within the three-way catalyst window, thereby reducing pollutant emissions. The fuel-to-air equivalence ratio overestimation that suffers the wide-range λ-sensor upstream three-way catalyst in the presence of short circuit is especially relevant. In this study, a novel approach to deal with the fuel-to-air equivalence ratio control under short-circuit conditions is introduced. Under this scope, this work proposes a strategy for the on-board correction of the aforementioned fuel-to-air equivalence ratio overestimation, by means of the information regarding short-circuit level that provides the frequency content of the λ-sensor at the engine frequency. Finally, the potential of this approach to minimize pollutant emissions, in particular the NO x penalty arisen as a consequence of running the engine under leaner conditions than expected, is assessed through experimental tests.

Development of a wide range-operable, rich-lean low-NOx combustor for NH3 fuel gas-turbine power generation

Low-NOx NH3-air combustion power generation technology was developed by using a 50-kWe class micro gas-turbine system at the National Institute of Advanced Industrial Science and Technology (AIST), Japan, for the first time. Based on the global demand for carbon-free power generation as well as recent advances involving gas-turbine technologies, such as heat-regenerative cycles, rapid fuel mixing using strong swirling flows, and two-stage combustion with equivalence ratio control, we developed a low-NOx NH3-air non-premixed combustor for the gas-turbine system. Considering a previously performed numerical analysis, which proved that the NO reduction level depends on the equivalence ratio of the primary combustion zone in a NH3-air swirl burner, an experimental study using a combustor test rig was carried out. Results showed that eliminating air flow through primary dilution holes moves the point of the lowest NO emissions to the lesser fuel flow rate. Based on findings derived by using a test rig, a rich-lean low NOx combustor was newly manufactured for actual gas-turbine operations. As a result, the NH3 single fueled low-NOx combustion gas-turbine power generation using the rich-lean combustion concept succeeded over a wide range of power and rotational speeds, i.e., below 10–40 kWe and 75,000–80,000 rpm, respectively. The NO emissions were reduced to 337 ppm (16% O2), which was about one-third of that of the base system. Simultaneously, unburnt NH3 was reduced significantly, especially at the low electrical power output, which was indicative of the wider operating range with high combustion efficiency. In addition, N2O emissions, which have a large Global Warming Potential (GWP) of 298, were reduced significantly, thus demonstrating the potential of NH3 gas-turbine power generation with low environmental impacts.

A study on combustion characteristics under enriched-oxygen condition by exergy analysis

The object of this paper is to investigate the effect of operating parameters on Oxygen-enriched combustion (OEC) by exergy balance analysis during methane combustion process. In this work, the specific exergy value of fuel, feed gas and products were calculated on the basis of the second law of thermodynamics in different reaction conditions, so that availability destructions and exergy efficiencies of OEC process can be obtained based on exergy balance, and the influence of initial fuel temperature, oxygen concentration, exhaust gas recirculation ratio and equivalence ratio were addressed. It is observed that during methane OEC process, the exergy efficiency is mainly affected by products temperature, in the case of products temperature lower than 1870K, exergy efficiency of combustion increase with products temperature, and opposite changes was appeared when the products temperature higher than 1870K. Meanwhile, appropriate control of equivalence ratio can also be used to improve exergy efficiency by suppressing the dissociation of product.

운전조건 변화가 HCNG 엔진용 삼원촉매 전환효율에 미치는 영향

Abstract - Stoichiometric combustion engine with Three-way catalyst had an advantage that can reduce the harmful emissions effectively. Fuel equivalence ratio controlled from engine is very important because Fuel equivalence ratio with high conversion efficiency was narrow. This study analyzed the conversion efficiency under whole range of operating area for to evaluate the performance of three-way catalyst. In order to identify the Optimum conversion efficiency, the conversion efficiency due to change the control value of fuel equiv-alence ratio was investigated. The result show that conversion efficiency of emissions(more than 95%) has dis-covered by means of fuel equivalence ratio control at each test condition. As engine power increases, optimal fuel equivalence ratio tended to increase linearly under operating conditions of similar exhaust gas temperature. Key words : HCNG(Hydrogen- Compressed Natural gas Blends), stoichiometri c, TWC(Three-way Catalyst), conversion efficiency, equivalence ratio

Closed-loop equivalence ratio control of premixed combustors using spectrally resolved chemiluminescence measurements

A control system based on a multiwavelength chemiluminescence sensor has been developed and tested to adjust the operating point of an optically accessible, lean premixed methane/air burner operated under pressures up to 20 bar and equivalence ratios ranging from 0.5 to 1.2, as typically found in premixed gas turbine combustors. The sensor comprises a broadband, low-resolution grating spectrometer scanning the light emitted by the burner in the range 250–850 nm. Spectral distributions, are analyzed in real time to determine the equivalence ratio according to a novel method described in this paper. Radical emission data in the form of intensity ratios OH * /CH * and CO 2 * /CH * are first measured during an, off-line combustor identification step carried out with the same monochromator. These data are collected in a lookup table, which is then used to monitor the equivalence ratio and control the fuel mass flow rate. Closed-loop control using this chemiluminescence sensor has been tested over a broad range of, operating conditions. The performance of the sensor and control system is assessed by simulating changes in fuel quality and by operating the system with contaminated windows. Equivalence ratio control was successfully achieved under all of these conditions, showing that a suitable processing of multiwavelength data allows premixed gas turbine combustion control.

Digital Control of Equivalence Ratio using Chemiluminescence Feedback for a Continuous Combustor

Recent pollution requirements and stringent operating conditions for gas turbine engines has prompted the need for real-time feedback control of combustion processes for power production and propulsion. NO and CO pollutants from gas turbine engines have been die focus of many researchers for some time. By accurately controlling the equivalence ratio (EQR), fluctuations to disturbances may be avoided so as to maintain desired levels of NO and CO. In this paper, we develop a feedback technique based on CH chemiluminescence for real-time control of EQR in combustion processes. We focus on a continuous combustor for experimental modeling and implementation. An in-depth presentation is given of model development and digital controller design. An experimental step response and pressure disturbance test is provided for experimental validation of the EQR controller. Equivalence ratio control produces over a 700% decrease in NO emissions for large pressure disturbances. A 1.18 second settling time with only 6.7% overshoot is achieved for EQR commands.