Quieter, cleaner diesels

A new combustion process and fuel injection system reduces emissions, fuel consumption and noise

By using rapid prototyping, computer and mathematical modelling, and structural analysis, Varity Perkins has developed a range of four-and six-litre naturally-aspirated, turbocharged and turbo-aftercooled, emissions controlled diesel engines with a power band stretching from 51.5kW to 134kW. The range incorporates 98 ratings, each within the requirements of Stage 1 off-highway emissions.

The new Perkins 1000 series engine is designed to perform throughout its operating range free of visible smoke. The rotary fuel injection system ensures that fuel is used in the most economical manner.

Off-highway emissions control regulations due to come into force between now and the end of the decade are exceeded by the new engine. This has been achieved by the introduction of the `Fastram’ combustion process. Advantages offered include reducing the environmental impact of diesel exhaust gas emissions, while delivering increased work effort without a fuel penalty.

The re-entrant Fastram combustion chamber takes air pre-conditioned by swirl induced within the cylinder head; then during compression, the conditioned air accelerates over the piston crown to enter the combustion chamber at a very high velocity. The lip of the combustion space was profiled so that the chamber turns the swirling air into areas of macro and micro-turbulence, ready to receive and burn fuel.

The pre-mix burn period is reduced, while the diffusion burning phase is faster. The result is that injection occurs later, and peak temperatures are reduced. As the rate of cylinder pressure rise is lower – as is the peak cylinder pressure – engine noise is reduced by up to 3dBA, resulting in an engine that is 50% quieter.

A rotary distributor fuel pump is pin-timed to ensure absolute accuracy on injection and provide the 20% higher injection pressures needed for cleaner emissions. Optimal fuel delivery is provided by 17mm, five-hole, valve covered orifice (vco) injectors. A spray pattern is created which ensures low smoke and emissions and low fuel consumption. Injectors are of the gland nut type, screwed in place and accurately located with a sprint-loaded ball.

A surface model of the pre-swirl port was used to create a mould core. Rapid prototyping enabled a cylinder head to be produced in six weeks and checked with structural analysis. CFD ensured the combustion space proportions were right to ensure more fuel was converted into power and less wasted to exhaust gases.

High grade, cast-iron, uni-flow cylinder heads are used on both four-cylinder and six-cylinder models. Both feature near-vertical, more centralised injectors and helical porting to input swirl-conditioned air. Multi-layered sliding gaskets ensure high integrity gas sealing between the head and manifold.

Reliable unaided cold-starting is provided down to -15 degreesC. After firing, engines run up to operating speed without white smoke. For extreme conditions, assisted cold starting functions down to -30 degreesC.

Torque shows an 11% improvement on the previous range, and it is possible to provide a torque rise of up to 33%. Dual-zone torque offers high torque and fast torque rise for difficult conditions, while high torque with progressive rise is automatic in normal conditions.