Modeling and simulation of hydrogen combustion in engines

doi:10.1016/j.ijhydene.2013.10.097

International Journal of Hydrogen Energy

Volume 39, Issue 2, 13 January 2014, Pages 1122-1136

https://doi.org/10.1016/j.ijhydene.2013.10.097 Get rights and content

Highlights

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Behavior of ignition delay for hydrogen-oxygen mixtures was validated.
•
Detonation initiation, degeneration and reestablishing were simulated numerically.
•
Peculiarities of deflagration to detonation transition were resolved.

Abstract

Hydrogen being an ecological fuel is very attractive now for engines designers. It is already actively used in rocket engines. There exist plans to use hydrogen in pulse detonation engines. However, peculiarities of hydrogen combustion kinetics, the presence of zones of inverse dependence of reaction rate on pressure, etc. prevent from wide use of hydrogen engines. Computer aided design of new effective and clean hydrogen engines needs mathematical tools for supercomputer modeling of hydrogen–oxygen components mixing and combustion gas dynamics.

The paper presents the results of developing verification and validation of mathematical model and numerical tool making it possible to simulate unsteady processes of ignition and combustion in engines of different types and to study its peculiarities. First, verification and validation of the chemical kinetic models for hydrogen oxidation were carried out through investigations on the ignition delay time on pressure, temperature, and equivalence ratio for hydrogen-oxygen mixtures. Then, the developed solver was used to model pre-mixed and non-premixed combustion and detonation related phenomena including deflagration to detonation transition.

Introduction

Rocket engines using hydrogen-oxygen mixture have the following peculiarity. On injecting liquid components fuel (hydrogen) having much lower critical temperature comes pre-evaporated and pre-heated in combustion chamber, while oxygen could be liquid then evaporating inside the chamber. Thus contrary to most types of engines hydrogen engine has an inverse mixture entering combustion chamber, in which fuel is gaseous and oxidant is liquid. However, taking into account rather low critical temperatures for both components estimates based on models developed in papers [1], [2], [3] show, that phase transition will take place in an order of magnitude faster then for hydrocarbon fuels. That provides the reason to use one phase model as a first order of approximation. Onset of detonation being very dangerous for classical RAM engines could, however, serve the basis for creating new generation of engines – pulse detonating engines (PDE) [4], [5]. For this issue the problems of detonation onset, decay and deflagration to detonation transition should be simulated quite accurately, because these processes strongly depend on inlet conditions, mixture composition and geometrical characteristics of combustion chamber [6], [7], [8].

Hydrogen chemistry modeling is rather complicated because regular kinetic mechanisms have hundreds stages. Many reduced kinetic mechanisms were developed. However, peculiarities of hydrogen combustion kinetics, the presence of zones of inverse dependence of reaction rate on pressure, makes developing reduced mechanisms a very difficult task, which was studied by many researchers [9], [10], [11], [12], [13], [14]. In the present paper kinetic models developed based on CHEMKIN package methodology [15] will be used. The validation of these models will be performed based on experimental investigations of ignition delay times being functions of pressure, temperature and mixture composition [16], [17]. The developed code will be used for simulation of premixed and non-premixed combustion and detonation related phenomena, including detonation onset, degeneration and deflagration to detonation transition.

Section snippets

Mathematical model

Numerical investigations of the DDT processes were performed using the system of equations for the gaseous phase obtained by Favre averaging of the system of equations for multicomponent multiphase media. The modified k-epsilon model was used. To model temperature fluctuations the third equation was added to the k-epsilon model to determine the mean squared deviate of temperature [7], [8]. The production and kinetic terms were modeled using the Gaussian techniques [18], [19].

The governing

Verification and validation of kinetic model

Validation of the model will be performed based on the analysis of ignition delay times for hydrogen-oxygen mixtures measured experimentally for different conditions: pressure, temperature and mixture composition. Ignition delay is a notation characterizing in experiments the time interval between mixture is placed under definite conditions and active energy release beginning accompanied by temperature and pressure growth. Ignition delay are often measured in shock tube experiments behind

Verification of the code in solving detonation onset problem

A test problem of detonation onset in premixed hydrogen–oxygen system initiated by energy release in a small ball shape volume in a cylindrical vessel was investigated using the developed code. The problem statement is the following. A cylindrical vessel 1 m diameter and 1 m long is filled in by stoichiometric mixture of hydrogen and oxygen at a given initial pressure p₀ and temperature T₀; initial velocity equals to zero. A ball shape volume in the axis of symmetry close to one of the walls

Combustion chamber with coaxial injection of oxygen and hydrogen

Diffusion combustion onset in a model combustion chamber was simulated numerically. Oxygen was delivered through the inner nozzle, hydrogen was delivered through the ring-surrounding nozzle. The schematic picture of the computational domain and the grid are shown in Fig. 7.

The problem statement was axis-symmetric. The computational domain was 3-D. The geometry was chosen to verify the numeric scheme and study accumulation of errors bringing to the loss of symmetry. Simulations were performed

Detonation decay and re-initiation on entering wider chamber

The control of detonation onset in large chambers is of major importance in pulse detonating devices. The advantages of detonation mode of energy conversion over constant pressure combustion bring to the necessity of promoting the onset of detonation and shortening the pre-detonation length.

The deflagration to detonation transition (DDT) and further transmission of detonation wave into the large combustion chamber turned out to be the key factor characterizing the Pulse Detonation Engine (PDE)

Deflagration to detonation transition (DDT)

Among all the phenomena relative to combustion processes deflagration to detonation transition is, undoubtedly, the most intriguing one. Deflagration to detonation transition (DDT) in gases is relevant to gas and vapor explosion safety issues. Knowing mechanisms of detonation onset control is of major importance for creating effective mitigation measures addressing the two major goals: to prevent the DDT in case of mixture ignition, or to arrest the detonation wave in case it was initiated. The

Conclusions

Predictive modeling 3-D code was developed making it possible to simulate chemically reacting turbulent pre-mixed and not pre-mixed flows. The code resolves hydrogen combustion chemistry in a sufficient way to model anomalous behavior of ignition delay times versus pressure. Within one and the same solver it was made possible to model establishing slow diffusion and kinetic combustion modes, as well as onset of detonation modes, and resolve deflagration to detonation transition mechanisms.

Acknowledgments

The authors gratefully acknowledge financial support from the Russian Foundation for Basic Research (RFBR Grant 11-03-00213).

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