Lanz Bulldog

Scheme of an Akroyd engine: 1 – hot-bulb ignition device, 2 – cylinder, 3 – piston, 4 – crankcase; the unlabelled part on the left is the exhaust

The Lanz Bulldog was built with a single-cylinder, two-stroke Akroyd engine – the so-called Bulldog engine – that was designed by Fritz Huber. The Bulldog engine was installed horizontally, with the ignition device – the hot bulb – facing forward. It has crankcase scavenging, and intake ports instead of valves. Due to its few moving parts – the piston, crank assembly and flywheel, the fuel injection system and oil system are the only parts that move – it was simple to manufacture, operate and maintain. In the Bulldog engine, fuel is sprayed under low pressure onto the hot-bulb ignition device, where the fuel is ignited and gradually undergoes combustion. This makes the Bulldog engine thermodynamically inefficient, but it requires neither a carburettor like an Otto engine, nor high compression like a Diesel engine. It does not require a special fuel to operate; it can burn regular fuels like diesel fuel or petrol, but also a wide variety of low grade fuel oils – even waste oils. This made the Bulldog engine reasonably economical to operate, despite its high fuel consumption. The original Bulldog had evaporative cooling. Later models use a thermosiphon cooler. For starting, the ignition device has to be heated to ignition temperature using a blow torch, then the engine is hand-cranked with the steering wheel.[1] Late Bulldog engines have a redesigned hot-bulb with direct injection; they were offered with electric glowplugs and an electric starter motor. Lanz sold these as "Halbdiesel" (half diesel) and "Volldiesel" (full diesel) models, albeit that the engine was not a diesel engine. The Bulldog engine was made with various different displacements, with the 4.8 and 10.3 litre versions being the most common ones.

• 130 mm × 170 mm, 2256 cm³
• 140 mm × 170 mm, 2617 cm³
• 145 mm × 170 mm, 2807 cm³
• 150 mm × 210 mm, 3711 cm³
• 160 mm × 190 mm, 3820 cm³
• 160 mm × 210 mm, 4222 cm³
• 170 mm × 210 mm, 4767 cm³
• 190 mm × 220 mm, 6238 cm³
• 210 mm × 210 mm, 7274 cm³
• 190 mm × 260 mm, 7372 cm³
• 225 mm × 260 mm, 10338 cm³

A 1939 model of Lanz Bulldog 8506, still built around a hot bulb engine.

A 1939 model of Lanz Bulldog D7506/3.

Model T01 from I.A.M.E. made in Argentina.

Bulldogs were also produced in Spain by Lanz Iberica S.A. at Getafe near Madrid. A total of 17,100 tractors were built from 1956 to 1963.

The Bulldog design was copied in other countries by several different manufacturers. While some of these copies were legitimately produced under license from Bulldog, most of them were built with each respective builder's own frame and body design, being powered by unlicensed copies of the patented Bulldog hot-bulb engine. Some of these examples are:

The Bulldog was similar to other European hot-bulb tractors that were being produced around the same time. Some of these examples are the SF Vierzon from France, the Landini tractor from Italy, and the HSCS from Hungary. The Field Marshall that was produced in England, was a similar design to the Bulldog hot-bulb engine with the exception of an internally designed vaporing plate which replaced the conventional externally located hot-bulb, this internal design required ignition papers in place of the external blow lamp to start the engine.