Engine combustion and performance literature

Alicat instrumentation used in engine combustion and performance research

Alicat has been cited in over 1,000 peer-reviewed research papers. The following papers focus on engine combustion and performance and emerging technologies in that field. Contact us if you’d like your research to be highlighted.

Sealing performance of a turbine rim chute seal under rotationally-induced ingestion

Abstract

This study focuses on the sealing capability of a turbine rim seal subject to hot gas ingestion driven purely by the rotor disc pumping effect rather than that induced by mainstream features such as vane and rotor blade passing. The aim is to provide useful data for conditions in which rotation dominates, and to clarify the flow physics involved in rim sealing. Experimental measurements of sealing effectiveness for a chute seal are presented for the first time without and with an axial, axisymmetric mainstream flow external to the seal. The test matrix covers a range of rotational Reynolds number, Reø, from 1.5×106 to 3×106, and non-dimensional flow rate, Cw, from 0 to 4×104 with the mainstream flow (when present) scaled to match engine representative conditions of axial Reynolds number, Reax.

(a) Mainstream and purge air feed supply, (b) Sealing effectiveness measurement system

(a) Mainstream and purge air feed supply, (b) Sealing effectiveness measurement system

Results from steady pressure and gas concentration measurements within the rotor-stator disc cavity and the rim seal gap are presented and compared to published data for other seal designs. Sealing performance of the chute seal is somewhat similar to that of axial clearance seals with the same minimum clearance.

Reference

Bru Revert, A., Beard, P. F., Chew, J. W., & Bottenheim, S. (2020). Sealing performance of a turbine rim chute seal under rotationally-induced ingestion. Journal of Physics. Retrieved 2021, from https://iopscience.iop.org/article/10.1088/1742-6596/1909/1/012035/meta.

Experiments and low-order modelling of intermittent transitions between clockwise and anticlockwise spinning thermoacoustic modes in annular combustors

Abstract

Annular combustion chambers of gas turbines and aircraft engines are subject to unstable azimuthal thermoacoustic modes leading to high amplitude acoustic waves propagating in the azimuthal direction. For certain operating conditions, the propagating direction of the wave switches randomly. The strong turbulent noise prevailing in gas turbine combustors is a source of random excitation for the thermoacoustic modes and can be the cause of these switching events. A low-order model is proposed to describe qualitatively this property of the dynamics of thermoacoustic azimuthal modes. This model is based on the acoustic wave equation with a destabilizing thermoacoustic source term to account for the flame’s response and a stochastic term to account for the turbulent combustion noise. Slow-flow averaging is applied to describe the modal dynamics on times scales that are slower than the acoustic pulsation.

Under certain conditions, the model reduces formally to a Fokker-Planck equation describing a stochastic diffusion process in a potential landscape with two symmetric wells: One well corresponds to a mode propagating in the clockwise direction, the other well corresponds to a mode propagating in the anticlockwise direction. When the level of turbulent noise is sufficient, the stochastic force makes the mode jump from one well to the other at random times, reproducing the phenomenon of direction switching. Experiments were conducted on a laboratory scale annular combustor featuring 12 hydrogen-methane flames. System identification techniques were used to fit the model on the experimental data, allowing to extract the potential shape and the intensity of the stochastic excitation. The statistical predictions obtained from the Fokker–Planck equation on the mode’s behaviour and the direction switching time are in good agreement with the experiments.

Reference

Faure-Beaulieu, A., Indlekofer, T., Dawson, J. R., & Noiray, N. (2021). Experiments and low-order modelling of intermittent transitions between clockwise and anticlockwise spinning thermoacoustic modes in annular combustors. Proceedings of the Combustion Institute, 38(4), 5943–5951. https://doi.org/10.1016/j.proci.2020.05.008

Combustion characteristics of butanol‐Jet A‐1 fuel blends in a swirl‐stabilized combustor under the influence of preheated swirling air

Abstract

Biofuels are carbon-neutral alternative fuels, which have emerged as an important source of energy for the aviation industry to reduce greenhouse gas emissions. Butanol is considered an emerging biofuel with properties that are suited for application in gas turbine engines. It is traditionally produced through the fermentation process of biomass (acetone-butanol-ethanol fermentation). To examine the feasibility of butanol as operating fuel, the combustion characteristics of butanol and butanol/Jet A-1 blends are examined in a lab-scale swirl stabilized burner, with emphasis on the effect of preheating because of the variation of inlet air temperature during flight operation. To rich the constant air temperature to 150°C, the incoming air (main air) is preheated and investigated for various equivalence ratios.

Compared to neat Jet A-1, the flames of the butanol/Jet A-1 blends have shown a better effect on global emission characteristics with comparable temperature distribution on adding butanol to Jet A-1. A 50% butanol-loaded blends show a reduction of 29% CO and 24% NOx compared to neat Jet A-1 whereas 30% loading follows a similar trend, and the pollutant emission is slightly higher than the 50% blend case. Additionally, both 30% and 50% butanol blends show a comparable flame temperature distribution, which is higher than neat Jet A-1.

Reference

Kumar, M., Chong, C. T., & Karmakar, S. (2021). Combustion characteristics of butanol‐ jet a‐1 fuel blends in a swirl‐stabilized combustor under the influence of preheated swirling air. International Journal of Energy Research. https://doi.org/10.1002/er.7331

Investigating anode off-gas under spark-ignition combustion for SOFC-ICE hybrid systems

Abstract

Solid oxide fuel cell – internal combustion engine (SOFC-ICE) hybrid systems are an attractive solution for electricity generation. The system can achieve up to 70% theoretical electric power conversion efficiency through energy cascading enabled by utilizing the anode off-gas from the SOFC as the fuel source for the ICE. Experimental investigations were conducted with a single cylinder Cooperative Fuel Research (CFR) engine by altering fuel-air equivalence ratio (ϕ), and compression ratio (CR) to study the engine load, combustion characteristics, and emissions levels of dry SOFC anode off-gas consisting of 33.9% H2, 15.6% CO, and 50.5% CO2. The combustion efficiency of the anode off-gas was directly evaluated by measuring the engine-out CO emissions.

The highest net-indicated fuel conversion efficiency of 31.3% occurred at ϕ = 0.90 and CR = 13:1. These results demonstrate that the anode off-gas can be successfully oxidized using a spark ignition combustion mode. The fuel conversion efficiency of the anode tail gas is expected to further increase in a more modern engine architecture that can achieve increased burn rates in comparison to the CFR engine. NOx emissions from the combustion of anode off-gas were minimal as the cylinder peak temperatures never exceeded 1800 K. This experimental study ultimately demonstrates the viability of an ICE to operate using an anode off-gas, thus creating a complementary role for an ICE to be paired with a SOFC in a hybrid power generation plant.

Reference

Ran, Z., Longtin, J., & Assanis, D. (2021). Investigating anode off-gas under spark-ignition combustion for SOFC-ice hybrid systems. International Journal of Engine Research, 146808742110169. https://doi.org/10.1177/14680874211016987

Insights into flashback-to-flameholding transition of hydrogen-rich stratified swirl flames

Abstract

In this study, we investigate the flame stabilization behavior in hydrogen-enriched stratified swirl flames after the flame flashes back into an annular mixing tube with an axial swirler of swirl number 0.9. Two different modes of flame stabilization, namely intermediate stabilization and flameholding, are identified. For 80% or higher hydrogen enrichment of the fuel, the flashback is found to result in flameholding. Acetone-PLIF measurements are used to assess the equivalence ratio distribution in the mixing tube.

It is shown that the flow inside the mixing tube has intermittent presence of fuel-rich pockets. Furthermore, high speed laser diagnostic and simultaneous chemiluminescence imaging was carried out to understand the transition of flame propagation from the center-body boundary layer to the outer wall boundary layer. With the help of time-resolved images and simultaneous velocity fields, four different stages of flashback-to-flameholding transition were identified. It was noted that the bright flame kernels formed due to the flame’s interaction with fuel-rich pockets, impose significant deflection on the approach flow in the vicinity of the outer wall boundary layer. Acute-tipped narrow flame structures were found to anchor the flame on the outer wall. These flame structures were found to accelerate upstream upon reaching the fuel-rich regions in the outer wall boundary layer.

Reference

Ranjan, R., & Clemens, N. T. (2020). Insights into flashback-to-flameholding transition of hydrogen-rich stratified Swirl Flames. Proceedings of the Combustion Institute, 38(4), 6289–6297. https://doi.org/10.1016/j.proci.2020.06.017

Random forest machine learning model for predicting combustion feedback information of a natural gas spark ignition engine

Abstract

Engine calibration requires detailed feedback information that can reflect the combustion process as the optimized objective. Indicated mean effective pressure (IMEP) is such an indicator describing an engine’s capacity to do work under different combinations of control variables. In this context, it is of interest to find cost-effective solutions that will reduce the number of experimental tests. This paper proposes a random forest machine learning model as a cost-effective tool for optimizing engine performance. Specifically, the model estimated IMEP for a natural gas spark ignited engine obtained from a converted diesel engine. The goal was to develop an economical and robust tool that can help reduce the large number of experiments usually required throughout the design and development of internal combustion engines.

The data used for building such correlative model came from engine experiments that varied the spark advance, fuel-air ratio, and engine speed. The inlet conditions and the coolant/oil temperature were maintained constant. As a result, the model inputs were the key engine operation variables that affect engine performance. The trained model was shown to be able to predict the combustion-related feedback information with good accuracy (R2 ≈ 0.9 and MSE ≈ 0). In addition, the model accurately reproduced the effect of control variables on IMEP, which would help narrow the choice of operating conditions for future designs of experiment. Overall, the machine learning approach presented here can provide new chances for cost-efficient engine analysis and diagnostics work.

Reference

Liu, J., Ulishney, C., & Dumitrescu, C. E. (2020). Random forest machine learning model for predicting combustion feedback information of a natural gas spark ignition engine. Journal of Energy Resources Technology, 143(1). https://doi.org/10.1115/1.4047761

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