**1. Introduction**

20 Will-be-set-by-IN-TECH

36 Fossil Fuel and the Environment

Mariani, A., Morrone, B. & Unich, A. (2011). Numerical evaluation of internal combustion

Miao, H., Jiao, Q., Huang, Z. & Jiang, D. (2009). Measurement of laminar burning velocities

Nagalingam, B., Duebel, F. & Schmillen, K. (1983). Performance study using natural gas,

Prati, M. V., Costagliola, M. A., Torbati, R., Unich, A., Mariani, A., Morrone, B. & Gerini,

Prati, M. V., Mariani, A., Torbati, R., Unich, A., Costagliola, M. A. & Morrone, B. (2011).

Ridell, B. (2006). Malmö hydrogen and cng/hydrogen filling station and hythane bus project,

Ristovski, Z., Morawska, L., Ayoko, G., Johnson, G., Gilbert, D. & Greenaway, C. (2004).

Sierens, R. & Rosseel, E. (2000). Variable composition hydrogen/natural gas mixtures for

Ulleberg (2003). Modeling of advanced alkaline electrolyzers: a system simulation approach,

Wang, J., Chen, H., Liu, B. & Huang, Z. (2008). Study of cycle-by-cycle variations of a spark

ignition engine, *SAE Int. Journal of Fuels and Lubricants* 4: 328–338.

gas, *Science of the Total Environment* 323: 179–194.

*J. Hydrogen Energy* p. doi:10.1016/j.ijhydene.2011.10.082. Markstein, G. (1964). *Nonsteady Flame Propagation*, Pergamon Press.

*Energy* 34: 507–518.

*WHEC* .

33: 4876–4883.

*Hydrogen Energy* 8: 715–720.

gas-hydrogen blends, *WHTC* .

*Turbines and Power* 122: 135–140. Sørensen, B. (2005). *Hydrogen and Fuel Cells*.

*Int. J. of Hydrogen Energy* 28: 21–33.

spark ignition engines performance fuelled with hydrogen - natural gas blends, *Int.*

and markstein lengths of diluted hydrogen-enriched natural gas, *Int. J. Hydrogen*

hydrogen-supplemented natural gas and hydrogen in avl research engine, *Int. J.*

A. (2011). Combustion analysis of a sparl ignition engine fuelled with natural

Emissions and combustion behavior of a bi-fuel gasoline and natural gas spark

Emissions from a vehicle fitted to operate on either petrol or compressed natural

increased engine efficiency and decreased emissions, *Journal of Engineering for Gas*

ignition engine fuelled with natural gas-hydrogen blends, *Int. J. Hydrogen Energy*

Pressurised combustion is a very attractive clean coal technology due to increased energy efficiency and abated emission of pollutants resulting from application of combined cycles. There is a general agreement that nitric oxide emissions decrease with enhanced combustion pressure. However, for nitrous oxide, the reported results show a contradictory influence of pressure.

The mode of NO and N2O formation during coal combustion is far from being understood. The most difficult problem is the pathway of fuel-N conversion for primary nitrogenous species. The issue becomes simpler in case of char combustion, but even here fundamental questions remain. The uncertainty of NO modelling is emphasized by there being two quite different models to explain NO emission during char combustion: char-N is converted to NO with subsequent reduction of NO through a reaction with the char inner pores; alternatively, char-N is converted to HCN with negligible conversion to NO within the pores and subsequent conversion to NO outside the particle.
