THE VLB ENGINE & ITS FUELS

NOTE: This article is based upon practical tests carried out on the VLB engine. No attempt was made to quantify 'best' ratios as the intention and time-scale of the work did not call for precise scientific information to be resolved. Such work would have been carried out at a later date had this been possible.

The VLB engine will run at up to 20,000 RPM on standard petrol (gasoline) in a stable and useful (loaded) situation. The monitoring equipment set 20k as the ceiling, and no attempt was made to exceed this limitation.

Arc initiated combustion promotes adiabatic reactions at lower mechanical pressures due entirely to the act of 'burning' some of the fuel in order to raise the pressure (or more significantly the gas temperature) above the flash-point of the rest of the fuel. Pressure reduces entropy, temperature instigates reaction. Reduced entropy increases the reaction efficiency (releases more free energy).

The prototype dual piston petrol VLB engine worked well on diesel fuel up to around 10k, at which point, failure to ignite became a hazard. An 80:20 diesel / petrol mixture, on the other hand, restored the 20k performance objective.

Paraffin (kerosene) allowed around 14k before the onset of failure, but a 90:10 paraffin / petrol mixture again restored performance.

These results were obtained with no adjustments. That is to say, the engine could have been set up to run on either of the fuels without the need to add petrol, but would have required either higher compression ratios or increased boost from the compressor (or a bit of both, of course).

The explanation for the above results is simple enough and was predicted. The faster the engine speed, the less time there is for the igniter to effect the required pressure rise, and the less reactive the fuel, the more time is required.

Clearly, by adding a percentage of a lower flash-point fuel, not only that fuel which becomes directly affected by the igniter will react faster, but the lower flash point fuel beyond the igniter's influence, will effectively lower the adiabatic threshold of the rest of the fuel. From this it can be seen that the required percentage of lower threshold fuel is that which will raise the whole chamber into the adiabatic zone of the remaining fuel.

Monatomic fuels such as hydrogen, and pure single molecule fuels such as methane, have precise reaction zones. This makes the operating parameters of a VLB engine easy to establish. In fact, with the variable ratio compressor (supercharger) it is possible to program the ECU to evaluate and select the precise settings for optimum performance without any need for skilled human input.

Given an engine properly set up to match its fuel, the ideal is that the arc is applied at TDC. This means that no opposing forces are generated by the combustion process, and none of the combustion product is wasted as a result. At engine speeds up to circa 15k, this is achievable. Beyond 15k, the arc onset may be advanced with minimal negative results, because (like all non-spontaneous reactions) very little force is generated during the instigation phase. But, at engine speeds where the adiabatic threshold cannot be attained by the 'burning' of fuel, within the adiabatic zone period of time – the system will fail. From this, it can be gathered that the engine is best suited to fuel mixtures, and that the required ratio of low to higher flash-point fuels is a precise science.

Another aspect of the process concerns the calorific value of the fuel components, particularly with respect to the combustion duration. A fuel which contains a number of components, each of which has its own, different, flash-point temperature, will rely upon a chain reaction. Clearly, a fuel could be tailored to effect ultra rapid reaction (e.g. hydrogen) or a relatively slow reaction (e.g. lubricating oil + diesel oil + petrol). In all cases, however, for all practical fuels, the 'burn' and the 'power stroke' duration are never compatible.

Note: Some of the fuels tested on the VLB engine even dipped into the area of highly dissimilar and (seemingly) incompatible fuels, with very promising results. The results and methodologies of the experiments are, however, still subject to secrecy.

Irrespective of the fuel type, the spontaneous reaction never properly coincides with the enforced chamber volume. That is to say, that the forces generated by the combustion cannot be tailored to the chamber, even with respect to a single (practical) engine speed. The ideal solution to this problem is clear. What is required is that the excess force is collected by some device (a "spring" for example) and returned to the piston later in the stroke. Clearly, a steel spring is not an option. Quite apart from the engineering difficulties, resonance would completely defeat such an arrangement. On the other hand, a pneumatic chamber, which would allow the excess force to be absorbed and then returned to suit the expanding chamber, would be an entirely different matter. That such a chamber could be incorporated into the cylinder is also feasible. Which, of course, is exactly what the VLB engine does. Very Lean means that there is an excess of air in the chamber, which will not directly enter into the combustion reaction, and which will, by becoming further compressed by the expanding reaction products, thus store and return much of the energy. Of course, it is not 100% efficient - the gasses escaping from the exhaust port will carry heat away from the process. But, a pair of thermometers and a pair of gas-flow meters, are all that are required to establish the positive gains of the process. However, any losses due to energy retention by the gasses must be seen as minimal when set against the still burning fuel which escapes through the exhaust valve of conventional petrol engines. This is especially true at high engine speeds.

Note: The idea of using hydrogen as a fuel in a reciprocating piston engine, and not employing an excess of air (or some practical alternative?) to assist in the distribution of the resolved energy, is positively ridiculous!

Clearly, for any given practical compression / fuel combination, there will exist a percentage of the cycle time during which the ignition of some of the fuel (by means of the arc) will raise the mixture into the adiabatic zone. The VLB engine employs a sinusoidal linear to rotary conversion system, primarily, to maximise this period. A sinusoidal force curve can also, however, be shown to be more efficient with respect to minimising turbulence of the chamber gasses. This, in turn, evens out the 'rate of change' of the forces acting upon the pistons, reducing wasteful and potentially damaging harmonic distortion (shock) within the mechanical assembly.

Note: The need for turbulence within a cylinder in order to promote better dispersion of the fuel only applies to configurations where "remedial" action is required to compensate for inadequate dispersion in the first place. Turbulence, as an independent component, can never be shown to enhance efficiency.

The VLB injector 'action' is directly related to the pressure curve of the cylinder gasses. Quite simply, the pressure within the cylinder acts upon the (larger) face of an hydraulic piston (the motor plate) which is coupled to the (smaller) face of an inject piston. The precise geometry is dictated by the physical quantity / pressure of the charge. That this has to be tailored to a 'mean' charge / chamber pressure does not cause significant problems across the required practical speed range, but it does compromise performance enough to have warranted attention. Obviously, the injector's hydraulic system requires some 'resetting' device, and this is the area where compensation may be applied. The most sophisticated version of the injector employed pneumatic pressure to return the pistons for each stroke, to delay the onset of injection, and to regulate inject duration.

The VLB engine's ability to modify its inlet air pressure, its exhaust valve timing and duration, and its injection characteristics as described above, makes it suitable for an exceptionally wide range of fuels. The only components (apart from those pertaining to fuel storage and delivery) that cannot cover the entire range, being the injectors, which may be changed with little more difficulty than a spark plug.

Liquid LP gas is an ideal fuel for the VLB engine. All of the commercially available gasses can be catered for, and special injectors which will deal directly with the fuel in its liquid state have been tested. Even the problem of empty tanks, with 'gas' filled pipes running the full length of the vehicle, has been solved by entirely satisfactory, safe, and inexpensive engineering, which simply 'bleeds' the gas into the air inlet system.

High flywheel speeds increase engine performance as no other single component can. Speeds of 20k are not just attractive to racecar builders. Provided that the speeds are not obtained by wasting fuel and generating pollution, they are essential to all vehicle engines. A separate study, which deals with the practical significance of high flywheel speeds, is available.