Reducing Fuel Consumption

Reducing Fuel Consumption and Carbon Emissions

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The previous page offered a generalised summary of modifications that can be expected to result in boosting of locomotive performance.  This page focusses on the associated benefits of reduced fuel consumption and consequent reductions in carbon emissions.

Any modification that improves a locomotive’s performance (in terms of power output), is likely to reduce its specific fuel consumption (i.e. its fuel consumption per unit of work output).  And any reduction in fuel consumption will result in a reduction in carbon emissions.

Reducing fuel consumption and carbon emissions can be approached in two ways:

1. Improve combustion to increase the energy transferred from the fuel to the generation of steam;
2. Reduce Specific Steam Consumption, thereby reducing the consumption of steam and the fuel that is required to generate it.

Dealing with each in turn:

Improving Combustion: In the case of coal burning locomotives, combustion may be improved and fuel carry-over reduced by either:

• Fitting the firebox with a combustion chamber to increase its volume and thus increase the residence time of the fuel/air mixture in the firebox; or
• Converting the firebox to a Gas Producer Combustion System (GPCS).  This reduces the volume (and hence velocity) of “primary” air passing through the firebed and thereby reduce its ability to lift unburne fuel particles off the surface (and thence through the tubes and out of the chimney).  Instead an increased volume of “secondary” air is passed over the top of the firebed to burn off combustible gases generated in (and released from) the firebed.

In the case of oil burning locomotives, provided the firebox is large enough to allow complete combustion, and provided the fuel burner is well designed and operating efficienty, there should be no measurable fuel carry-over.

Specific steam consumption can be reduced through any or all of the following:

• Increasing steam pressure and/or superheat temperature.
• Fitting feedwater heater(s) so that more of the heat produced from the fuel can be used for creating steam.
• Minimizing resistance to steam flow into the cylinders – e.g.
  • by enlarging the main steam pipes and steamchest volume;
  • by streamlining valve ports, port edges, valve heads and edge lands, and steam passages;
  • by optimising clearance volume; and
  • by optimizing valve events, lead, lap and valve travel.
• Minimizing resistance to exhaust steam flow out of the cylinders – e.g.
  • by enlarging and streamlining valve ports, port edges, valve heads and edge lands;
  • by optimizing valve events, lead, lap and valve travel;
  • by optimising clearance volume;
  • by enlarging and streamlining exhaust steam passages;
  • by fitting a Kordina below the blast pipe;
  • by fitting an efficient (low pressure) exhaust system such as the Lempor or Lemprex.
• Minimizing steam losses through leakage e.g. by fitting multiple narrow rings to valves and pistons, and multiple element piston and valve rod glands
• Minimizing energy losses through condensation on cylinder walls through increased superheat temperature and/or improved insulation; and not operating at extremely short cut-offs;
• Minimizing incomplete expansion losses by optimising clearance volume and operating with fully open regulator and short cut-offs (but not so short as to result in condensation losses).
• Improving insulation around all hot surfaces to reduce heat losses.

Any of the above measures will result in a reduction of fuel and water consumption for any given duty.