Parkinson and Crosley introduced the principle of using air of greater density than that of the atmosphere, and so obtained an engine of greater power in the same compass. Each of them came with his own specific technology, and although the Stirling engine and the Parkinson & Crossley engines were quite similar, Robert Stirling distinguished himself by inventing the regenerator. These precursors, to whom Ericsson should be added, have brought to the world the hot air engine technology and its enormous advantages over the steam engine. The two Stirling brothers were followed shortly after (1828) by Parkinson & Crossley and Arnott in 1829. They inverted the design so that the hot ends of the displacers were underneath the machinery and they added a compressed air pump so the air within could be increased in pressure to around 20 standard atmospheres (2,000В kPa). Stirling patented a second hot air engine, together with his brother James, in 1827. Out of them came a new arrangement for a hot air engine. In this patent (# 4081) he describes the 'economiser' technology and several applications where such technology can be used. The Stirling 1816 patent was also about an 'Economiser', which is the predecessor of the regenerator. This experiment proved to the inventor that, owing to the low working pressure obtainable, the engine could only be adapted to small powers for which there was, at that time, no demand. ДЄ 2-horsepower (1.5В kW) engine, built in 1818 for pumping water at an Ayrshire quarry, continued to work for some time, until a careless attendant allowed the heater to become overheated. It was to it that the inventor devoted most of his attention. The principle of the Stirling Air Engine differs from that of Sir George Cayley (1807), in which the air is forced through the furnace and exhausted, whereas in Stirling's engine the air works in a closed circuit. Stirling came up with a first air engine in 1816. This engine type was of those in which the fire is enclosed, and fed by air pumped in beneath the grate in sufficient quantity to maintain combustion, while by far the largest portion of the air enters above the fire, to be heated and expanded the whole, together with the products of combustion, then acts on the piston, and passes through the working cylinder and the operation being one of simple mixture only, no heating surface of metal is required, the air to be heated being brought into immediate contact with the fire. Robert Stirling is considered one of the fathers of hot air engines, notwithstanding some earlier predecessors-notably Guillaume Amontons -who succeeded in building, in 1699, the first working hot air engine. Illustration from Robert Stirling's 1816 patent application of the air engine design that later came to be known as the Stirling Engine Early hot air engines However, contemporary investment in renewable energy, especially solar energy, has increased the efficiency of concentrated solar power. Originally conceived in 1816 by Robert Stirling as an industrial prime mover to rival the steam engine, its practical use was largely confined to low-power domestic applications for over a century. Strictly speaking, the inclusion of the regenerator is what differentiates a Stirling engine from other closed-cycle hot air engines. Closed-cycle, in this context, means a thermodynamic system in which the working fluid is permanently contained within the system, and regenerative describes the use of a specific type of internal heat exchanger and thermal store, known as the regenerator. More specifically, the Stirling engine is a closed-cycle regenerative heat engine with a permanent gaseous working fluid. A Stirling engine is a heat engine that is operated by the cyclic compression and expansion of air or other gas (the working fluid) at different temperatures, resulting in a net conversion of heat energy to mechanical work.

Heat exchanger gasket chart