A Review on Combustion Characteristics of Ammonia as a Carbon-Free Fuel

Jun Li,Noriyuki Kobayashi,Rongjun Wu,Hongyu Huang,Lisheng Deng,Danan Chen,Shini Lai

doi:10.3389/fenrg.2021.760356

Abstract

A comprehensive review of combustion characteristics of ammonia (NH3) as a carbon free fuel is presented. NH3 is an attractive alternative fuel candidate to reduce the consumption of fossil fuel and the emission of CO2, soot, and hydrocarbon pollutants, due to its comparable combustion properties, productivities from renewable sources, and storage and transportation by current commercial infrastructure. However, the combustion properties of NH3 are quite different from conventional hydrocarbon fuels, which highlight the specific difficulties during the application of NH3. Therefore, this paper presents comparative experimental and numerical studies of the application of NH3 as a fuel during combustion process, including the combustion properties of laminar burning velocity, flame structures, pollutant emissions for the application of NH3 as a carbon free fuel. This paper presents the burning velocity and pollutant emissions of NH3 alone and mixtures with other fuels to improve the combustion properties. The aim of this paper is to review and describe the suitability of NH3 as a fuel, including the combustion and emission characteristics of NH3 during its combustion process.

Highlights

With the rapid economic development and population explosion of recent decades, the global primary energy consumption has increased dramatically
The experimental results show an exponential variation of laminar burning velocity under different volumetric hydrogen fraction and the ammonia/hydrogen/air flame speed decreased with an increase in pressure under the same hydrogen concentration
The maximum value of laminar burning velocity is less than 10 cm/s, which is relatively low when compared with that of CH4/air flame

Summary

INTRODUCTION

With the rapid economic development and population explosion of recent decades, the global primary energy consumption has increased dramatically. The development of new technologies aiming to reduce problems related to energy consumption, for application in both developed and developing countries, has become urgent, because of the increasing strictness of governmental regulation of energy and CO2 emissions. Such developments lead to the search for carbon-free fuels, and the increasing importance of renewable energy sources (Astbury, 2008). It is necessary to have a comprehensive understanding of the combustion and emission characteristics of pure NH3 and mixture with other fuels, which are expected to supply power for transport vehicles, electricity for power generation, and heating for industry with suitable combustion properties in future energy system.

Upper flammability limit

NOX EMISSIONS

Findings

CONCLUSIONS AND PERSPECTIVES