The piston engine is still the only truly viable method of converting energy into motion. The overall requirements are contradictory and evolutionary. Plenty of mass-production blind alleys have been followed, but each has found its niche, and each deserve review at intervals as the world requirements change. An engine must today meet; stringent emissions standards, excellent fuel economy, low noise output, a flat torque characteristic across a large rev range, exceptional power-density, low mass, sensible production costs and longevity. 

There have been many engines that meet some of these requirements with ease, none that meet all. The R+D challenge is to meet them all by a holistc, interlinked approach to the whole engine design. The Villiers V10 engine and its derivatives set out to achieve that challenge.

EMISSIONS

Given up-to-date after treatment (close-coupled catalysts, etc.) most modern petrol engines are 98% clean when warm. It is start-up and warm-up that pose the biggest challenge. The Connaught engine has three-stage split cooling involving separate controlled water flows between the head and block (split-cooling patent), and “dry-start” cylinder heads whereby the combustion chambers are insulated by air-gap until up to temperature. This enables cold-start and acceleration fuelling to be withdrawn within three seconds of cranking at 15 degrees ambient.

It also enables the internal temperatures of both oil and coolant to be maintained after shut-down, allowing hot-start without extra fuelling. As a result, it would be the first vehicle to improve, rather than detract from, ambient emissions by shutting down in a traffic jam. Ultra close-coupled catalysts and localised air injection are temperature controlled by integral water jackets (see above). The first time this has been achieved. Closed-loop fuelling control can also be accomodated.  (See all items below as all affect emissions). 

FUEL ECONOMY

A petrol engine is at its least efficient at idle and part-load. It is therefore useful to shut-down when stationary (subject to the provisions of emissions, above), and to have a very high compression ratio to increase efficiency at part load. The choice of compression ratio is dictated by the surface to volume ratio of the combustion chamber (the smaller the better), the shape of the combustion chamber, and the bore to stroke ratio. A great deal of R+D has dictated a bore of 62.5 and a slightly longer stroke, giving 200cc/cylinder with a 2-valve chamber with pocketed exhaust valve. This enables some considerable valve overlap (for performance) without gas crossover between the valves (emissions) and a high mechanical compression ratio of 10.5:1 or more on low-grade fuel without risk of detonation. The biggest enemy to engine fuel economy is closed loop control (whereby the engine is over-fuelled continuously to force the catalyst into NoX reduction). Circa 20% of fuel is wasted in this way. An added big disadvantage is that, when the control system fails, the engines exhaust becomes dirtier than an engine from the 1930’s. On-going R+D involving further cooling system work, the possible introduction of the two-stroke cycle, and alternative after-treatment is destined to delete the closed-loop control and drastically improve fuel economy and emissions durability. See also “Flat Torque”, “Power density”,  “Hybrid System” and all other items as they also affect fuel economy. 

LOW NOISE

The biggest culprit for general noise emission is nowadays the cylinder block, which magnifies and radiates noise like a loudspeaker. Given that most blocks have two rectangular flat sides, the effect is stereoscopic. Clearly, the block must be designed to be as rigid and light as possible with the best possible thermal stability and bearing alignment, and with minimum internal windage.

The deep egg-crate external structure and internal cross-bracing fulfills all the requirements and emits no amplified noise whatsoever. Exhaust (and to a lesser extent, intake) noise are the second biggest noise generator. A single cylinder engine is worst, whilst muti cylinders get progressively quieter due to the self-cancelling effects and higher frequencies. This reflects on mass and package. More cylinders = less silencing = similar overall mass = different package requirement. See Power density and Mass.

FLAT TORQUE CHARACTERISTIC

All conventional internal combustion engines have a dip in the torque output at somewhere around 2500rpm (road engine). Variable valve timing by cam-shift goes some way to reduce this dip and the Connaught engine can be run with a cam-shift shuttle block mounted within the timing cover. However, this is nothing like as effective as fully variable, individual cylinder, valve timing by reed valves topped by individual throttles, all mounted as close to the inlet valves as possible. Despite fairly wild cam timing for performance and revs, the close-coupled nature of the reed valves eliminate back-flow, so volumetric efficiency (fuel economy and torque output) improves enormously in the lower rev-range. If the torque curve can be sufficiently boosted at low revs it becomes possible to “short-shift” to the next gear without detriment to performance but with a major improvement to fuel economy. If this is coupled with the Connaught Hybrid system it becomes possible to create a gearless and clutchless system whereby the engine rotates from zero rpm at zero mph to peak power at maximum velocity. This produces a genuinely giant improvement in fuel economy of over 20%. See Hybrid system. 

POWER DENSITY

Power density describes how much output one can get from the space all  the mechanical parts occupy. The masters of power density are the Formula 1 engine designers. Two-stroke and Wankel engines can also offer exceptional power density, and work is going on to further develop the engine to run on the two-stroke cycle. (See VCR). It is important for fuel economy and emissions to keep the thermal package as tight as possible. To achieve this considerable study was put into engine configurations. A 22.5 degree V allowed good balance in 4, 8 and 10cylinder configurations and reasonable balance in 6-cylinder form (with some offset mass in the flywheel and pulley arrangement). 22.5 degrees allows a very tight cooling package (See Emissions) and allows the oil/water intercooling system to be simply integrated into the block. However, such a tight package makes it impossible to install conventional crankshaft main bearings, so these bearings move to the outside of the crank webs. A vast amount of development involving materials, oil pressures and flows, floating bearings, number of bearings (4 in the V6 and 6 in the V10), etc has culminated in the adoption of a roller and ball bearing assembly for each. Thus friction and mass is minimised (and a smaller, lighter, starter motor can be installed).

MASS

This is an obvious requirement. The less mass in the static components, the less there is to be heaved around, the better the fuel economy. Likewise in the moving components. Less mass, less flyweight inertia, quicker response equals a more effective output and better economy and emissions. Unfortunately, the less mass there is the worse the NVH (noise/vibration/harshness) gets.  See Emissions, Economy, Noise, Power Density.

PRODUCTION COSTS and LONGEVITY

Initial costs are always, understandably, high. The requirement for lowest production costs often causes many of the special requirements to be abandoned at the design stage. If the future of the IC engine is to continue this attitude must change.  The uniqueness of this engine lies in the way well-proven manufacturing principles from all around the world have been brought together into one package. Testing, time and continued R+D will prove out the longevity.

HYBRID SYSTEM

A great deal of rubbish has been talked and written about “Hybrid Systems”. Basically, anything that can be made to go has to be made to stop, so some of the energy used to make it go can be recovered during the stopping. This has been known since the dawn of the motor car, but every attempt made has shown the fuel economy gains not to be economically viable. This position has now changed slightly due to the political climate. A hybrid system could be hydraulic, pneumatic, electric or any other combination. It happens that electric is currently on top. The very simple maths is as follows:- 3 litres of fuel are used to accelerate from zero to 70mph. The engine is 33% efficient, so 1 litre has actually done the accelerative work. We then use a regenerative braking system to come from 70 to rest (rather than converting the 1 litre’s-worth of heat energy that made us go into heat energy dissipated into atmosphere by conventional braking). But the regenerative system is around 33% efficient, so one third of a litre of “fuel” is put back into storage to help us “go” again. So out of 3 litres used we get 0.3 back to use again, or roughly a 10% improvement in fuel economy. 10% is worth having, but research shows that if the entire system mass exceeds 10% of the vehicle mass all the gains are lost. Therefore there are very few current production hybrid vehicles that show any significant fuel saving in mixed-use driving. The Connaught system is very different to any other, and is extremely effective under low speed and town conditions. As a result there are further gains to be had. 

In the introduction I mentioned a holistic approach. Assuming the 10% hybrid mass target can be achieved (in the Connaught case 90kg in 1000kg), thus making hybrid power addition worthwhile, it is possible to design the IC engine to take advantage of the off-line assistance. See “Flat Torque Characteristic”. With max hybrid-supplied torque available from zero rpm it is possible to start the IC engine in gear (in the case of the V10, in top gear) and pull away simply by pressing the throttle, all the way to top speed. Thus the engine idle condition is deleted and the engine runs in an efficient zone from the off. Furthermore, one of the biggest improvements to fuel economy is the ability to use tall gearing. Even in a conventional driving mode it is possible to short-shift into the taller gear very early on. This action alone delivers a further 10% fuel saving.

A FOOTNOTE TO TAKE US BACK TO THE BEGINNING.

Anyone who has tried to crank-start a 4-cylinder engine whilst in gear will know how the vehicle jumps and leaps down the road. Clearly this is unacceptable. The solution lies in multiple cylinders. The minimum acceptable with flywheels is 6, the best without flywheel inertia is 10. This clearly raises the spectre of internal friction negating the economy benefits, so here is an explanation of how it is accomodated. (See also Power Density). The roller and ball race bottom end is almost friction free and uses less energy running a low-pressure oil supply. Because the cylinder bores are small, single compression ring slipper pistons can be used. In the case of the 6 and 8 cylinder, ring friction roughly equals that of a 2.0 litre 4-cylinder, whilst cylinder sealing is marginally improved. However, the biggest justification for multiple small cylinders is the small surface to volume ratio (See “Fuel Economy”) which allows a higher compression ratio without detonation, the benefits of which exceed any frictional losses.