VLB ENGINE SYNOPSIS

Below is a list of features which together describe many of the differences between the VLB and conventional engines. The engine (though overall different to the norm, even to the point of being generally perceived as "oddball") departs from the norm only where such departure can be fully justified in terms of correcting known and generally accepted deficiencies in established technology. Items marked 'essential' indicate departures which interactively permit the engine to function more effectively over a wider power-band than any other known configuration. In addition to addressing the shortcomings of the conventional engine 'per se', the VLB engine design is optimised for vehicle use, and many of its features should be judged in that context. Perhaps of equal significance, the engine is ideal for use as an hydraulic pump, aiming at a gearbox and clutch free vehicle, where the throttle demand can be made to directly equate to required vehicle speed.

KEY FEATURES

1. 65% reduction in fuel consumption, with no loss of performance.
2. Zero unburned hydrocarbons, nitrous oxide and carbon monoxide.
3. Substantially reduced engine cost.
4. Substantially reduced engine and exhaust temperatures.
5. Non-consuming, low pressure dry sump lubrication system.
6. Essential circa twice the output power for half the engine weight.
7. Essential arc initiated spontaneous combustion.
8. Essential safe and stable 20,000 RPM flywheel speed.
9. Essential single cycle (two-stroke) operation.
10. Essential fuel supply controlled (open choke) operation.
11. Essential revised crank/piston geometry with sinusoidal velocity curve.
12. Essential revised gas flow path and control.
13. Essential high pressure air input system.
14. Essential direct fuel injection with unique mechanical servo control.
15. Essential and unique two-stage fuel modification system.
16. Essential enhanced fuel injection control system.
17. Essential integrated performance monitoring features.
18. Essential load sensitive, servo orientated ECU, with comprehensive diagnostic and early warning (compensating) failure features, which far exceed current design philosophy or capabilities.

THE CLAIMS

A 65% reduction in fuel usage with no reduction in performance sounds rather too much for many people. On the other hand, the claim relates to the vehicle, not the engine in isolation. Fully engineered, the VLB 'car' will weigh significantly less, mostly from reduced engine weight, but also due to significant reductions in chassis weight, and the obsolescence of a conventional gearbox and clutch. Some of the performance is also recovered in this way, as well as from increased efficiency between the pistons and the road wheels.

It is important to stress that the final VLB engine design owes more to extensive analysis and practical testing of a wide range of conventional engines than to original design. Indeed, the justifications for most of the departures from tradition can be established by direct comparison with conventional design, and its known and generally accepted deficiencies.

Without doubt, it was John Allen's long experience with race engines, which both created the initial inspiration, and provided much of the fundamental understanding of the limitations of conventional technology, all of which eventually led to the final configuration.

THE ENGINE

NOTE: The sketch "half.gif" is reasonably to scale, but is only intended to be 'functional'. It does not show details which would not serve this simplified description.

Referring to the functional sketch. This shows one half of a single 'motor', the piston assembly being duplicated to the left as indicated by the 'cut' con-rod. Two of these motors make up a standard four-cylinder configuration, one being attached to either side of the main shaft assembly (MSA) from which the drive (hydraulic) is taken. Each motor is a complete and functional unit, designed to be separately fitted to a dynamometer for testing and setting up.

The ultra-lightweight flat top pistons are fairly conventional, with regular upper, oil, and lower rings. The connecting 'rods' (lightweight tubes) are rigidly connected to the piston crowns at one end, and likewise to the converter oval at the other. Thus the two pistons are rigidly connected to each other, the whole assembly describing a single linear reciprocating motion.

Trapped within the centre of the transfer 'oval', is a roller bearing, which is fitted to one of the MSA's small flywheels. By this means, the pistons impart motion to the flywheel, and the flywheel regulates the pistons such that the velocity curve of both is sinusoidal. Two assemblies are possible: 90 degrees, where each of the four pistons fire at their own quarter revolution points, and: 180 degrees where the two motors fire in synch, but from opposite sides. The former provides a smoother power delivery, the latter, higher torque.

In addition to the load imposed by the flywheel, the underside of each piston provides the moving element of a compressor or 'supercharger' whereby air admitted by the lower cylinder inlet port (VECTIS) is pressurised before gaining access to the upper cylinder via the air transfer channel. The compressor loading of the piston, also promotes stability to the piston motion. The static element of the compressor is fitted to the converter housing by a fine screw thread. In its basic form, this is simply locked so as to provide a range of preferred input pressures, but the design also allows for the dynamic variation of the input pressure, both for heavy loading applications (heavy goods vehicles) as well as racing engine optimisation, and multi-fuel vehicles.

Note: With the vehicle in motion, the air arriving at the inlet port is already significantly raised above atmospheric pressure by the VECTIS (q.v.).

The significance of the imposed sinusoidal velocity curve is that it extends the period that the pressurised combustible mixture is in what we call the adiabatic zone. That is, a pressure where ignition of the richer 'upper' mixture will further raise the cylinder pressure above that required to effect spontaneous reaction of the remaining fuel. Clearly, the work required of the piston in order to compress the gasses is less than it would be if (as in a diesel engine) it alone was required to reach the necessary adiabatic pressure. The mechanism also ensures that the velocity curve of the pistons match that of the flywheel, removing the harmonic distortion which plagues high flywheel speed conventional engines. Note that the design also hands the precise moment of the reaction over to the ECU, which varies it according to flywheel speed and load.

The exhaust valve or valves are positioned at the top of the cylinder. Air in at the bottom, exhaust out at the top, create the ideal gas-flow characteristics, absolutely essential if the gains from higher flywheel speeds are to be realised.

Note: To fully appreciate the above gas-flow benefits, one should refer to the massive two-stroke diesel engines use by locomotives, etc.

The fuel mixture is directly injected at the top of the cylinder, during the compression stroke. Pressure from within the cylinder, via a mechanical amplifier, is the motive force behind the injection, ensuring an evenly graduated fuel input, which becomes widely distributed throughout the gas. The initialisation pressure, and the injection response curve are also dynamically modified by the ECU, depending upon flywheel speed and load.

At or very near TDC, the richer upper fuel mixture is subjected to an electronically produced 'arc', using two conventional narrow-gauge spark plugs. The burn is limited only to the time that is taken to reach the adiabatic pressure, whereupon all of the remaining fuel is spontaneously converted. No "flame front", as such, is encountered with respect to the combustion process.

Note: The engine will run with single plugs. The second is included as a cheap way of avoiding failure at very high flywheel speeds. Indication is given, and performance reduced, in the event of a plug failure.

The VLB engine is a single cycle (two-stroke) perfectly balanced, supercharged, adiabatic machine, with a significantly reduced piston compression load. In addition, the fuel air distribution is better than is achieved by any low compression indirect or direct injection system - far less loaded and with enormously better organised combustion than the most sophisticated diesel engine - with significantly better power to weight and fuel conversion than any two stroke - yet employing the best features of each.

The exhaust of a properly set up VLB engine is cooler and cleaner than any conventional engine, and does not require a catalytic converter.

Each half of the engine has its own flywheel, the two being connected by a central 'main shaft'. Drive is taken from this central shaft, the preferred mechanism being an hydraulic pump, of which the shaft forms an integral part.

Mainly due to the lean fuel / air mixture, but aided by other factors, the exhaust and engine temperatures are significantly lower than any of the conventional engine, permitting entirely adequate air cooling and consequential engine weight reduction and loading. Heat pipe technology is employed to provide ultra-light and self regulating temperature control. A separate article dealing with this subject is available.

Lubrication is of the dry sump variety, but employing lighter oils at significantly lower pressures than other engine types.

The fuel conditioning system is such that the calorific value, the innate self-dispersing nature, and the spontaneous temperature threshold, of the 'charge', can be varied by the ECU. This aspect of the design is currently still subject to secrecy.

The pneumatic or hydraulically operated exhaust valve is independently controlled (by the ECU) according to requirements.

The air inlet system is fed via a "volumetric efficiency correcting tuned induction system" (VECTIS) and the engine runs in true "open choke" mode (except at tick-over). This mode ensures that no cycle fails to reach total burn conditions, and no fuel is wasted by the unavoidable 'information lag', inherent to throttle control systems.

Note: The VECTIS system is a "ram-air" concept, an idea which can be traced back at least to the 1920s. But it was an idea that had to wait for John Allen's design skills and deep understanding of engineering, to become a practical performance enhancing reality. John introduced it to UK production saloon car racing in 1993. Within a single year, it had become an essential standard throughout the entire saloon car racing world.

The separate control over the fuel injection and exhaust valve features is also harnessed to enhance engine braking, efficient enough to effect an emergency stop under total brake failure conditions, or more normally, to save fuel on the overrun, without having to employ compromising and complicated bypass systems.

The flywheels safely reach speeds of 20,000 RPM, due to the significantly enhanced anti-vibration nature of the design, as well as to the reduced number of independently moving parts, the improved gas-flow characteristics, the fixed nature of the air and fuel inlet systems, and the ECU's designed ability to detect and avoid resonance and load related harmonic distortion - in particular, when used in conjunction with hydraulic, auto-gearing, transmission systems. (Note. Although 20,000 seems very fast by modern road engine standards, the VLB engine is expected to reach 40,000 with further development).

Not shown in the drawing, the motion converter oval outer edges run in oil slides. These provide an oil transfer mechanism for the cylinder via wick-filled channels and small bore inner pipes. The slides also critically dampen potentially damaging resonance of the reciprocating assembly.

Each flywheel drives its own small oil pump, which supplies both the engine unit proper, and its (self-aligning roller type) main bearing. The flywheels also contain wick-filled oil channels, which supply the converter roller bearing units by employing centrifugal force.

In the event of an engine failure (which does not immobilise) the damaged half of the engine can be rendered inoperative by shutting off the fuel supply and holding the exhaust valves open (in sympathy with the pistons) thus reducing the compression cycle to a near zero workload. Under these conditions, the vehicle may be comfortably driven (albeit at reduced power) to a place of safety or repair.

THE ECU

The VLB engine is heavily biased towards flexibility. Indeed, much of its ability to improve upon existing technology arises from a pre-design analysis of how the availability of intelligent control can be used to maximise such flexibility. The ECU is essentially a servo (feed-back) orientated design, allowing it to make adjustments, not only by sensing conventionally monitored data, but by detecting changes indicated by sounds and vibrations picked up by ceramic microphones. To this end, many of the components have been configured to assist the process by embodying unique "sound" evolving characteristics.

Servo tendency (trial and error) techniques are also extensively employed by the ECU, in order to maximise performance over the widest possible range of operating conditions, even to the point of being able to compensate for failing components (whilst limiting performance, and communicating the situation to the driver, of course).

Unlike most dedicated processor applications, the VLB ECU employs a highly structured and flexible 'operating system' similar (in principle, at least) to that employed by computers. By this means, a single basic unit may be reprogrammed or extended in order to accommodate additional engine and vehicle fittings or improvements. By the same token, the vehicle can be quickly and inexpensively changed to suit different fuels (albeit sometimes using different injectors).

There is even a facility to select between maximum performance and minimum fuel consumption, with a number of in-between settings, and with 'auto-override', if the driver floors the throttle.

GENERAL

So thorough is John Allen's particular (possibly unique) approach to design, that production requirements, servicing and repair, value engineering, and even 'end user' perception, all played an important part in the design's evolution. Driveability, for example, was gauged against racing standards. Serviceability and repair took account of facilities within the economic scope and skill levels of the smallest engineering workshops. The extent to which this "integration" is incorporated is hard for many people to grasp. John claims that design evolution, at least within the limits of available technology, should be a theoretical process (albeit finely honed by way of suitable practical experimentation) and not the severely limited modification and 'add-on' process that is more normally practised.

THE HISTORY

John first conceived the possibility of a spark initiated adiabatic gasoline engine way back in the late 1970s, when he tested a turbo-charged racecar with indirect fuel injectors. The engineer who had assembled the engine had left out the head spacer plate required to reduce the C/R for turbo operation, and the custom (separate coil for each plug) ignition system had failed, causing the spark to occur at TDC.

The engine took a lot of starting, but it did finally fire up and John was able to go out on track. Within about 20 seconds the car was flying like nothing that he or his crew had ever witnessed before. The first lap was absolutely incredible, but alas, the car didn't make it back to the pits, second time round. Once John had figured out what had happened, he became determined to find a way of stabilising the process.

The first true VLB engine ran in 1990. The configuration that is detailed here was built in 1992. In 1995, John was made bankrupt as a direct result of all lean-burn engines being outlawed by the US government.

What more is there to say?

Mick Adshead

With my thanks to: John Allington and Rosemary Allen