Rotating Cylinder Valve (RCV) engine unveiled

Until the 1990s forest and garden products were unregulated in terms of exhaust emissions but since this time, progressively tighter levels of regulation have been enforced by both the California Air Resources Board and the US Environmental Protection Agency. Small, piston-ported two strokes were formerly the power unit of choice for this industry. These offered advantages of high power to weight ratio, reliability and crucially for a cost-driven market, simple and low cost manufacture. Unfortunately they also tend to have the limitation of comparatively high fuel consumption and poor hydrocarbon and CO2 emissions.

RCV technology provides an ideal solution for hand-held equipment manufacturers aiming to replace two stroke units. It provides the inherent emissions advantages (both regulated and CO2) of a four stroke but offers a robustness, reliability and high power to weight ratio in a highly revving engine with a package size more typical of a two-stroke engine; all crucial advantages for hand-held equipment. Moreover it offers the potential for low-cost manufacture which is particularly attractive in this highly competitive and price-sensitive market.

Premium performance at low manufacturing cost

The RCV engine concept has been shown to offer the potential for both high performance and fuel economy, as well as for low emissions. While these are attractive attributes for prospective customers of products powered by RCV engines, it is important for manufacturers that these benefits can be delivered in a cost-effective manner. The results of a detailed study carried out by RCV Engines Ltd based upon manufacturing data provided by MPI, show that the projected performance/manufacturing cost trade-off of an RCV engine is significantly better than that of a range of existing successful products (see chart below). Based on this analysis there is a clear, near-linear relationship between performance and manufacturing cost for the existing production engines. However, the projected performance/cost trade-off of a similarly sized RCV engine is significantly better than this trend. The analysis shows that it is of similar manufacturing cost to that of a conventional single overhead camshaft, two-valve per cylinder air-cooled engine. Crucially however, the RCV engine delivers more than 20% additional specific power. Products powered by RCV engines are thus likely to have market appeal with the ability to deliver premium power compared to competitor engines of similar capacity and production cost.

RCV offers better volumetric efficiency

The RCV engine concept has a number of inherent advantages compared with a conventional two- or four-valve per cylinder four-stroke engine. Firstly in terms of combustion, an RCV engine’s configuration enables a much larger port cross-sectional area than is practicable in a poppet valve engine, which has the effect of significantly improving its volumetric efficiency. The design of the port and combustion chamber – including the large squish area at the piston crown – also generates a very high level of intake air turbulence which is conducive to efficient combustion. These advantages provide significant improvements in performance across the speed range; in effect combining the positive attributes typically associated with two-valve per cylinder four-stroke combustion at low engine speed, with those of a four valve per cylinder design at high speed.

Secondly the rotating cylinder valve and its seal, which rotate at half crankshaft speed, are extremely dynamically stable. With adverse valve train dynamics typically the limiting factor for the maximum operating speed of conventional poppet valve four-stroke engines, RCV technology enables reliable and durable operation at much higher speeds than might be the case for an equivalently sized conventional engine. The combined effect of these advantages enables RCV engines to consistently deliver performance in excess of 100PS/litre (75kW/litre).

The stable and efficient combustion system of an RCV engine, combined with the elimination of losses normally associated with operation of the valve train, provides the potential for improved fuel consumption in addition to superior performance. Naturally, the balance of these benefits in a given product will be optimised in accordance with each manufacturer’s marketing strategy. Some for example may use the advantages of RCV technology to enable aggressive down-sizing in order to deliver equivalent power and performance from a smaller capacity and more fuel efficient engine. Others however, may favour its use to deliver premium performance characteristics over and above those of existing products. For motorcycles and scooters in particular, such ‘fun to drive’ characteristics may be considered advantageous in attracting customers within a highly competitive consumer-driven market.

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