Akroyd Stuart or Diesel?


With regard to John Stickland's letter expressing interest in the engines of Pool, Diesel and Akroyd (note correct spelling) Stuart. Over the last 60 years internal-combustion engine specialists have devoted a great deal of time to who was first with the compression ignition engine, Diesel or Akroyd Stuart. However what should be realised is that these two innovators were in no way in direct competition as their products differed considerably.

Herbert Akroyd Stuart was born' in 1864 in Halifax and raised in Bletchley, Bucks. His father ran the Bletchley Iron & Tin Plate Works. So after working as a junior assistant in the Mech. Eng. Dept. of the City of Guilds of London Technical College, Finsbury, Herbert joined his father at the Iron Works. He devoted his time to developing a paraffin vaporising engine and took out his first patent in 1886, followed by a more relevant patent in 1890. So it is beyond dispute that he had a satisfactory "oil engine" before Diesel. Basically what Akroyd Stuart had invented was "automatic-ignition", because prior to 1890, oil engines required a blow lamp to be permanently in contact with the vaporiser while in motion. Akroyd Stuart arranged the vaporiser and engine cycle in such a manner that the lamp could be removed as soon as the engine was started, the combustion chamber then maintained a high enough temperature by heat retained from previous explosions assisted by the heat of compression of air. When the "air only" was compressed into the already hot vaporiser, the ignition was controlled by timing the injection of the oil spray near the end of the compression stroke which obviated somewhat but not completely the pre-ignition troubles which worried oil engine manufacturers at that time. The compression pressure used in his early engines was only in the region of 40/50 lb. sq. in. In later years this type of engine operation became known as "hot-bulb" or "surface-ignition" and more unfortunately the term "semi-diesel" was used. All these terms especially the latter, robbed the inventor of the right amount of credit due to him.

Rudolph Diesel aimed at developing an engine with the highest possible efficiency and several years of theory had taught him that in order to do this, he would have to compress the air to the highest degree possible. He was well aware that fuel injected into highly compressed "red hot" air would burn without any ignition devices at all, or need any form of pre-heating to obtain the first explosions. In one of his first engine tests, a compression temperature off 500°C was seen when using a compression of  425 lb./sq. in. In 1893 the first trials of Diesel's engine began. Surely here is the true term "compression ignition" engine. As so often happens with great innovators, prophets and the like, neither men ended their days reaping the fruits of the part they had played in the evolution of the successful oil engine. Akroyd Stuart, MIMechE, after selling his patents to Richard Hornsby & Co., constantly had to defend his invention against the  name of semi -diesel when he claimed it should have been "Akroyd-cycle". He emigrated to Australia in 1899 and died there in 1927. It seems a pity that his great engineering achievements seem to have been forgotten with the passing of time disappeared. However it appears that Pool was rated as one of the better than average innovators, in fact it is said that more than one competitor visited Chipstable in the hope of seeing something useful! It is however · very doubtful if he had any association with Akroyd Stuart as the latter's ideas for automatic ignition came about because of an accident which took place in the Bletchley workshop.