Clean Technologies and Environmental Policy

, Volume 21, Issue 1, pp 167–178 | Cite as

Effect of water injection into the intake manifold on combustion and NOx emissions of CHP engine fuelled with natural gas

  • Omar I. AwadEmail author
  • H. Arruga
  • Hai Tao
  • F. Scholl
  • M. Kettner
  • M. Klaissle
  • Rizalman Mamat
Original Paper


The impact of variable water injection by mass on nitrogen oxide emission and performance characteristics of combined heat and power single-cylinder spark ignition engine fuelled by natural gas under constant power was investigated. For each water/fuel ratio, the combustion phasing was varied by adjusting spark timing and mass of fuel injection to maintain the indicated mean effect pressure at 6.35 bar. It was reported that the nitrogen oxide emissions decreased with the same centre of combustion when the amount of injected water increases. The nitrogen oxide emission averagely decreased by 20–25%, depending on combustion phasing with water/fuel ratio 0.3 compared to 0. Furthermore, the centre of combustion between 15 and 19 °CA after top dead centre represents lower nitrogen oxide emissions. It was recorded that the spark timing had to be advanced with water injection to maintain the indicated mean effect pressure at 6.35 bar. Also, the results of the effects of intake manifold water injection system on performance, combustion and emissions at the lowest level of the nitrogen oxides have been presented. The thermal efficiency and indicated specific fuel consumption were improved with water injection at an operation point compared with a reference point. The maximum nitrogen oxide reduction depends on the maximum water injection rate which is limited by intake air characteristics.

Graphical abstract

NOx emission for various WI rates over the centre of combustion CA50


CHP SI engine Nitrogen oxides (NOx) emission Intake manifold water injection Natural gas combustion 



After top dead centre


Brake-specific fuel consumption


Before top dead centre


Brake thermal efficiency


Center of combustion


Center of combustion


Combined heat and power


Carbon monoxide


Carbon dioxide


Coefficient of variation


European Environment Agency


European Union




Internal combustion engine


Indicated mean effect pressure


Indicated specific fuel consumption


Nitrogen oxides


Water/fuel ratio


Water injection



The authors would like to thank the German Federal Ministry of Education and Research, which supported this project through the grant programme “Ingenieurnachwuchs”, as well as all the persons that were involved in the project.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Universiti Malaysia PahangGambangMalaysia
  2. 2.Karlsruhe University of Applied SciencesKarlsruheGermany
  3. 3.Baoji University of Arts and SciencesShaanxiChina
  4. 4.SenerTec Kraft-Wärme-Energiesysteme GmbHSchweinfurtGermany
  5. 5.State Key Laboratory of Automotive Safety and EnergyTsinghua UniversityBeijingChina

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