Steam diesel hybrid locomotive

In outline the machine resembled a conventional 2-6-2T steam locomotive, but it had four pairs of horizontally opposed cylinders (13½ inch bore × 15½ inch stroke—343 × 394 mm) mounted longitudinally above the frame and driving a crankshaft placed between them, with the further drivetrain by gears.[2] The cylinders were made double-ended, with the rod end of each cylinder for steam and the closed end fitted with a diesel injector. (Some drawings, published in contemporary magazines, show only two pairs of cylinders and it seems that this was one of the design features that was changed during development.) The boiler, with a diameter of only 51 inches (130 cm) and a small internal firebox, was mounted above. The "regenerator", capturing heat from the exhaust, was integral with the boiler and had 38 tubes totalling a heating area of 508 sq ft (47 m²). The driving position was in the usual place behind the boiler, and tanks—400 imperial gallons (1,800 litres) for fuel and 1,000 imperial gallons (4,500 litres) for water—were mounted on the frame at the rear, one above the other.[1]

The sequence of operation began with heating the boiler in the normal way, but using fuel oil instead of coal. The start from rest was made with steam power, but at about five mph (8 km/h) the diesel injectors were started and the steam turned off. The waste heat from the cylinder jackets and diesel exhaust then maintained the boiler in steam for auxiliary functions (brakes and whistle) and in readiness to supplement the diesel power if required, or for the next start. The temperature of the water jacket, maintained at considerably above boiling point, assisted the compression ignition of the diesel fuel and only a relatively low compression ratio was required.[3] Because steam power provided the torque required for starting, no form of variable transmission was necessary and a permanent reduction geartrain of ratio 1·878 to 1 was fitted.[1]

Overall power output (800 bhp under diesel, 1,000 bhp when supplemented with steam)[2] did not compare well with conventional steam locomotives, although the performance on gradients was good because of the gearing. During the trials it was used successfully with coal trains and it proved very efficient in terms of fuel used, because the waste heat from the diesel power was recovered. However its running costs depended on the price differential between coal and oil and this was not favourable. When Kitson & Co. failed in 1934 the LNER handed the machine back to the company's receivers and it was dismantled.

The Soviet Union built three large experimental locomotives between 1939 and 1946.[7]

The first prototype, numbered 8000, a 2-8-2 from the Vorishilovgrad works, had two pairs of outside double-acting opposing pistons; when diesel power was initiated, at about 20 km/h (12 mph), diesel fuel was injected into the centre portion between the pistons which thus became the compression-ignition chamber, while the outer ends of the cylinders continued to receive steam in the normal way. Although the unit remained in passenger service, intermittently, until 1946, when it was tested again. It was put into storage in 1948. It was not considered a success as its 25-tonne axle load was too high, it rode hard on the tracks and was prone to cracking cylinders.[8]

TP1-1, the second prototype (illustrated right), under the name of Сталинец (Stalinets), was a cab-forward condensing 2-10-2 from the Kolomna works, used gas produced from an anthracite coal plant in the tender to fuel its spark-ignition internal combustion cylinders, along with anthracite pulverised in the gasification plant to heat the boiler. There were a total of eight pistons in four cylinders in an opposed-piston configuration; two steam cylinders and two coal gas cylinders. It was reported to have only functioned properly at speeds of 25–30 km/h and below as travelling faster for about 10–15 minutes would cause the gas mixture to combust prematurely when entering the combustion chamber. Issues were reportedly sorted out by 1941 but the project was abandoned during Operation Barbarossa and the outbreak of WW2 on Soviet territory.[7][8]

Number 8001, the third experiment, also named Сталинец, was a unit developed from the previous Voroshilovgrad design in 1946. It was also a 2-10-2 configuration and had the centre space in the cylinders, between the opposed pistons, intended to combine compression ignition and steam expansive working in the same chamber. It was reportedly almost a complete disaster and placed in storage in 1948.[7][8]

In 1925, Jakob Buchli of Switzerland obtained US patent 1559548 for a combined steam and internal-combustion engined locomotive. This differed from the Kitson-Still system in that there was no waste heat recovery and the steam and internal combustion engines had separate cylinders (vertically mounted in the tender), but both driving the same traction wheels. Buchli specified that "…the steam generator is supported upon one vehicle…and the steam and internal combustion engine cylinders together with their driving gear are carried by a separate truck or vehicle". His proposal was for the "steam generator vehicle" to be in the form of a traditional steam locomotive boiler with driver's cab, but without pistons. A "flexible pipe" would lead steam to the pistons within the "detachably coupled…truck" (tender). His claimed advantages were the reduced complexity of a combined transmission system, the improved comfort of the operators being separated from the driving cylinders and the differing maintenance requirements of steam and diesel (such as boiler washouts) being more easily accommodated when the units were detachable.[9] It is not known whether any locomotives to Buchli's design were actually built.

In 1954 Chicago inventor Charles Denker patented a system whereby the exhaust from a conventional four-stroke diesel engine was directed into a large-diameter steam cylinder. There was no boiler: instead a pump, operated by a cam driven from the common crankshaft, injected water (warmed by the diesel cylinder water jacket) into the steam cylinder so that it was instantly evaporated by the hot exhaust gases, powering the piston by expansion. Again, no operational examples are known.[10]