Boosting Loco Performance
Boosting Locomotive Performance
|Note: It is not recommended that any modifications be carried out that increase an existing locomotive’s tractive effort without proper engineering analysis. Increasing tractive effort is likely to result in forces in the locomotive’s motion, frames, drawgear etc. for which they have not been designed. Thus if, for example, any increase in boiler pressure is proposed (to improve thermal efficiency), it may be wise to reduce cylinder diameter such that the original nominal tractive effort is retained.|
Note: On page 144 of his book, Wardale makes the point that in the broader meanings of the words Performance and Efficiency, reductions in maintenance and increases in reliability are just as relevant as improvements in power output and fuel economy. Notwithstanding, this page and the following three pages relate to the narrower meanings of these terms.
It is difficult to separate out individual “modernization” options in order to achieve specific goals, since the adoption of one may (and often does) necessitate the adoption of others. For instance, increasing superheat temperature to raise thermal efficiency is likely to require improvements to the lubrication system and redesign of valves and valve liners to prevent temperature-induced breakdown of lubricants.
Bearing the above in mind, this and the following pages aim to simplify the options by listing those that should help to meet specific requirements – in this case boosting locomotive performance.
Boosting locomotive performance is best achieved by increasing its thermal efficiency (as compared to simply increasing energy input and thus fuel consumption) since increasing efficiency results in extra work output from any given fuel input.
One of Porta’s favourite equations offers another way of illustrating this:
This shows that power output will be increased by boosting steam production and/or by reducing specific steam consumption.
Steam production may be increased through any or all of the following:
- Increasing heat output from the firebox by increasing combustion airflow through the use of a more efficient exhaust system, including where possible the fitting of a Kordina, bearing in mind that the grate limit may need to be increased by converting the firebox to GPCS operation.
- Increasing heat transfer between combustion gases and boiler water by maximising the number of tubes and optimising the ratio of flues and tubes.
- Fitting feedwater heater(s) so that more of the available heat is used for evaporation.
- Improving insulation around the boiler to reduce heat losses.
Specific steam consumption can be reduced through any or all of the following:
- Increasing steam pressure and/or superheat temperature.
- 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 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 including 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 minimising clearance volume and operating with fully open regulator and short cut-offs (but not so short as to result in condensation losses).
Thus increased performance may be obtained by implementing any or all of the above.