Free Piston Engines

Free Piston Engines

ABSTRACT

The research of the free piston engine is taking up pace since the last two decades mainly carried by the Dutch companies NOAX and the Innas.The research in free piston engines has recently concentrated on hydraulic versions but some development in electric version has also been reported.

This seminar mainly discusses the case study of the CHIRON (Pronunciation ky’-rahn) Free Piston Engine, which is a hydraulic free piston engine developed by the Dutch companies Innas, and NOAX. CHIRON in the Greek mythology was a Centaur: neither a horse nor a man but a synthesis of a man and a horse. Similarly, the CHIRON discussed in this paper is neither an engine nor a pump: it is a combination – or better – an integration of an engine and a pump.

In CHIRON the combustion energy is directly converted in to Hydraulic energy. The CHIRON features direct electronic control of the injection parameters, the flow and the compression ratio. The flow output is controlled by means of Pulse Pause Modulation of the piston frequency. The CHIRON is designed for the common pressure rail systems. In these systems, the hydraulic energy is supplied through a common rail. Special attention will be paid specific characteristics of the CHIRON compared to conventional engines and pumps.

INTRODUCTION

Complexity is never a goal in designing a new product. Products are designed to have low fuel consumption and reduced emissions and most importantly to satisfy customers. Yet, the products are complex though the simpler solutions are feasible.

A good example is the motor pump combination one can find on site machines. In these machines, the energy of the combustion process is converted in to mechanical energy by means of a piston. On the other side, the mechanical energy is converted in to hydraulic energy by translating piston. If we are able to connect the combustion piston directly to the hydraulic piston, then we can eliminate all mechanisms in between. This would then result in the ‘free piston engine’. However the currently the engine and pump are defined as two separate machines, both having rotating shaft to connect one machine to the other. This problem arises due to the reasons that the hydraulic industry is relatively young and when hydraulic motors and pumps arrived in the market, the crankshaft engine, mechanical drives and the electric motor had already defined a quasi standard; the rotating shaft. The hydraulic industry had to adapt to this ‘standard’, especially since in most cases the hydraulic systems were seen as an accessory, leaving the main drive functions to gears, chains and belts. Furthermore, the diesel engine was already produced in large quantities and there was no reason to construct a new engine for the small beginning hydraulic market.

Nevertheless, many attempts have been made to design and built a combination of an engine and a pump without the mechanical complexity of piston rods and crankshafts. Since the combination of the combustion piston and the hydraulic plunger is not connected to a mechanism, and the combined piston has the degree of freedom in the axial direction, these machines are called as the ‘free piston engines’.

However, in the hydraulic free piston engines unlike the conventional pumps these engines have a pulsating flow output. By means of hydro pneumatic accumulator the flow pulsations can be filtered very effectively. Accumulators however act as an integrator slowing down the pressure response. The recent development of a new hydraulic transformer called the IHT (Innas Hydraulic Transformer) offers a way out for this problem

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