I have been trying to estimate the flow rates, working pressure and hence the required power so we can spec our combustion engine, however this is proving difficult without having a good simulation of the hydraulic system.
We have a copy of Festo's Fluidsim, which is an easy to use fluid suimulation package, however, there are some major limitations when it comes to simulation inputs to control loops. Although this has given me an approximate idea of flow, I really need to get a more realistic figure.
Currently Im estimating a flow rate of 120 to 160 lpm at a working pressure of 160 bar. With these figures and a fudge factor for efficiency of 20% this would require and engine capable of delivering:
(120 lpm x 160 bar) * 1.20 / 600 = 38.4Kw
(160 lpm x 160 bar) * 1.20 / 600 = 51.2Kw
For various reasons we have opted for a Diesel engine, predominately due to the high torque output at low revs which is better suited for hydraulic pumps.
There are many engine below 35Kw to choose from, but there seems to be very few in the 40 to 50Kw range. Its clear however, that in order to get the power we require at a reasonable size and weight ratio, we will need a turbo charged engine.
I'm currently looking at Deutz and Perkins engines, both have a good selection of industrial power units which will be great for our needs: an engine with all the gubbins apart from muffler and fuel tank ready to bolt to our chassis.
Neither Josh or myself have much knowledge of engines, which is why we need a simple off the shelf solution. There are probably much more powerful cheaper car engines we may be able to use, but without the experience, we are opting for an turbo diesel industrial power unit.