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Steam Locomotion in the 21st Century

The Recent History of Steam Locomotive Development

Steam Locomotive Exhaust Design

updated 2 February 2022

The sound, smell, and sight of the exhaust of a steam locomotive is undoubtedly its most memorable aspect. Interestingly, the exhaust system is a crucial part of the design of a steam locomotive, and one which dramatically affects its performance for better or worse. Around the world, from the late 1800's through the first half of the 20th century, a great deal of attention was focused on the design of the exhaust systems for steam locomotives. Unfortunately, in most countries steam locomotive development ceased about the same time that research in the fields of engineering related to gas flow and nozzles exploded. Since WWII, much research and development has been performed in these areas as a result of the development of jet powered aircraft and rockets.  The scientific knowledge which could have led to significant improvements in steam locomotive exhaust design only came about just as interest was waning in steam locomotive development.

In the late 1940's and after, Ing. L. D. Porta intensely studied steam locomotive exhaust design, applying scientific principals which led to further improvements.  This resulted in his Lempor (Lemaitre-Porta) and Kylpor (Kylala-Porta) exhausts used during his early work in Argentina.

The first notable paper on steam locomotive exhaust design published by Porta was with his contemporary Ing. Claudio S. Taladriz titled "The Exhaust of Locomotives", in 1957. This paper is provided courtesy of Jos Koopmans, translated into English by Porta's son D. L. Porta from a manuscript in Phil Girdlestone's collection.

The Exhaust of Locomotives by Ing. Livio Dante Porta and Ing. Claudio S. Taladriz (NEW 18 January 2014)

Perhaps the most famous publication on steam locomotive exhaust system design is Ing. L. D. Porta's Lempor Theory.  It was first published as a technical paper in 1974, and describes his Lempor Ejector exhaust system.  The complete Lempor Theory is available here:

Theory of the Lempor Ejector as Applied to Produce Draught in Steam Locomotives by Ing. L. D. Porta

Porta contacted me personally through this webpage some years ago and requested that I publicize this theory as much as possible and request review and comments from knowledgeable engineers who might be able to suggest improvements or refinements to this theory.
One of the few people who took up this challenge was Jos Koopmans (PhD) of the Netherlands who made the study of locomotive exhaust systems his engineering doctorial thesis.  The work he did for his thesis led him to write the book "The Fire Burns Much Better" which documents steam locomotive exhaust design from the earliest steam locomotives through the present day.  Jos developed his own theory for locomotive exhaust design which has been used to design replacement exhaust systems for several steam locomotives, including this one:  Excerpts from the book and additional information are available at:

Also included is a series of photos of the Kylpor Exhaust system (later superceded by the Lempor), developed by Ing. Porta from the Kylchap exhaust system of Chapelon.   These photos can be accessed here:

Photos of Kylpor Exhaust system of 2-10-2's of the Rio Turbio line in Southern Argentina

This section provides an overview of steam locomotive exhaust system development in the 20th century, showing some of the many configurations/designs that have been tried:  Exhaust System Drawings & Photos

In the last years of his life, Porta was working on a further development of the Lempor exhaust, the Lemprex. While only limited information has been made public on this system, it focused on improving ejector performance within the limited height available on many steam locomotives by trying to improve steam/gas mixing within the "mixing chamber" portion of the ejector.  It is believed that the exhausts installed on the Donna Teresa Christina Railroad in Brazil during Porta's work there in the early 1990's incorporate elements of his Lemprex exhaust system.  Information and photos on these engines, including the exhaust systems, is available here:  Porta proposed the Lemprex for his improved UK A1 steam locomotive design as well.

Interestingly, Porta's final word on locomotive exhaust design was not his own Lempor Theory.  On the 5AT Project pages, David Wardale mentions that the preliminary design for the exhaust system for the 5AT was based on a technical paper on the design of ejectors (not specific to steam locomotives) published in 1972, which Porta had brought to his attention.  This document is "The Prediction of the Optimum Performance of Ejectors", written by Professor JAC Kentfield and R. W. Barnes and published by the Institute of Mechanical Engineers in the UK.  This paper is available through the IME at this address (registration required for search):