https://orcid.org/0000-0001-7551-6923
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ABSTRACT
Compression ignition engines are more dominant in automotive sector than spark ignition engines due to higher torque and better fuel efficiency. However, nitrous oxides and particulate matter are the main emissions from the CI engines. Hydrogen is used as an alternative fuel due to its high diffusivity, high flame speed and wide flammability limits. Elevated levels of nitric oxide emissions are the main concern with the usage of hydrogen as a fuel. In order to meet the requirements of present-day emission standards, many control techniques are developed. This article categorises the available NOx emissions control strategies into pre-intake, in-cylinder and post-combustion techniques. A summary of various methods are presented to control the NOx emissions from literature with hydrogen as a main fuel. Intake temperature, intake pressure, exhaust gas recirculation, O2 concentration, air fuel ratio, addition of inert gases, water and steam injection are discussed in pre-intake control strategies. In-cylinder control strategies like varying compression ratio, swirl and injection timing are studied. Various post-combustion control strategies like SCR, urea injection, Vanadia sublimation, hydrocarbon SCR, lean NOx trap, SCR lean trap NOx are explained.
Nomenclature
| NOx | = | Nitrous oxide |
| CO | = | Carbon monoxide |
| CO2 | = | Carbon dioxide |
| HC | = | Hydrocarbon |
| UHC | = | Unburnt hydrocarbon |
| PM | = | Particulate matter |
| O2 | = | Oxygen |
| O3 | = | Ozone |
| CI | = | Compression ignition |
| H2 | = | Hydrogen |
| NO2 | = | Nitrous dioxide |
| NH3 | = | Ammonia |
| NO | = | Nitric oxide |
| NC | = | Phenyl iso-cyanide |
| HCN | = | Hydrogen cyanide |
| OH | = | Hydroxide |
| CH | = | Methylidyne radical |
| CH2 | = | Methylene |
| C | = | Carbon |
| C2 | = | Carbon radical |
| CN | = | Cyanide |
| NO2* | = | Activated nitrous oxide molecule |
| BTE | = | Brake thermal efficiency |
| EGR | = | Exhaust gas recirculation |
| BSFC | = | Brake-specific fuel consumption |
| CR | = | Compression ratio |
| CC | = | Combustion chamber |
| DEF | = | Diesel emulsion fluid |
| ASC | = | Ammonia slip catalyst |
| PGM | = | Precious group metal |
| SiO2 | = | Silicon dioxide |
| TiO2 | = | Titanium dioxide |
| SO2 | = | Sulphur dioxide |
| Cu-Z | = | Copper–Zinc |
| Fe-Z | = | Iron–Zinc |
| V2O5 | = | Vanadium pentoxide |
| WO3 | = | Tungsten oxide |
| CFD | = | Computational fluid dynamics |
| DOC | = | Diesel oxidation catalyst |
| Al2O3 | = | Aluminium oxide |
| SCR | = | Selective catalytic reduction |
| HC SCR | = | Hydrocarbon selective catalytic reduction |
| GHSV | = | Gas hourly space velocity |
| Cu-ZSM-5 | = | Cu-Zeolite Socony Mobil-5 |
| LNT | = | Lean NOx trap method |
| Pt | = | Platinum |
| Pd | = | Palladium |
| CNG | = | Compressed natural gas |
| HCNG | = | Hydrogen compressed natural gas |
| SWC | = | Specific water consumption |
| BMEP | = | Brake mean effective pressure |
| HES | = | Hydrogen energy share |
| CAD | = | Crank angle degrees |
| bTDC | = | Before top dead centre |
| aBDC | = | After bottom dead centre |
| Nm | = | Newton metre |
| ppm | = | Parts per million |
| HCCI | = | Homogeneous charge compression ignition |
| RCCI | = | Reactivity controlled compression ignition |
| PCCI | = | Premixed charge compression ignition |
| DDM | = | Diesel dual fuel mode |
| BDM | = | B20 dual fuel mode |
| WDM | = | Water injection dual fuel mode |
| RDM | = | Retarded injection dual fuel mode |
| EtOH30 | = | Blend fuel with 68vol% gas oil, 29vol% ethanol and 3vol% octanol |
| EtOH50 | = | Blend fuel with 48vol% gas oil, 48vol% ethanol and 4vol% octanol |
| HCE | = | Hydrogen combustion efficiency |
| HMF | = | Hydrogen mass fraction |
| Symbols | = | |
| ↑ | = | Increases |
| ↓ | = | Decreases |
| = | Forward reaction | |
| ↔ | = | Reversible reaction |
| Ф | = | Fuel–air equivalence ratio |
Disclosure statement
No potential conflict of interest was reported by the authors.
Additional information
Funding
Notes on contributors
Sirajuddin Syed
Sirajuddin Syed is pursuing the doctor of philosophy in the area of diesel engines with renewable fuels such as hydrogen. He has prior working experience in teaching and now continuing with the full time research work on computational and experimental studies on compression ignition engine with diesel as maiin fuel and hydrogen as additional fuel via induction in a vortex tube.
Manimaran Renganathan
Manimaran Renganathan is working as an Associate professor in the Thermal and Automotive Research Group, School of Mechanical and Building Sciences of Vellore Institute of Technology, Chennai, India. He has published many research articles and also currently undertaking a research project on compression ignition engine with hydrogen as an alternative fuel. He is mainly involved in the enhancement of fuel-air mixture formation studies using vortex tube. His interests include computational fluid dynamics, heat transfer, internal combustion engines and experimental fluid dynamics of underwater robots.