Thursday 27 August 2015

I4 engine with the performance of a V8

A research programme in the US is pulling together various technologies to create a four-cylinder engine with the performance of a V8.

The programme, expected to be complete by the end of 2017 and funded by the Department of Energy, is making use of variable compression ratio, variable valve timing, supercharging and compacted graphite iron (CGI).

Project lead is in the hands of Envera LLC of Los Angeles, California with Eaton Corporation acting as a joint partner contributing relevant advanced technology R&D as a cost-share partner.

The researchers are expecting to achieve an output of 283kW from the 2.4-litre engine which is equivalent to 118kW/litre and a brake specific fuel consumption of 234g/kWh. A torque of 440Nm is claimed.

The high efficiency VCR engine funded by the US Department of Energy is worth $2,784,127, is due to be completed in 31 December 2017.

The engine uses variable compression ratio from 8.5 to 1 to 18.1, variable valve timing to cater for Atkinson cycle and various supercharging settings and advanced supercharging to create high ‘launch’ torque and pow standby losses.

The aim is to achieve a 25 per cent improvement in fuel economy over a standard spark ignition engine and 40 per cent better “mileage” than a V8 powered van or pickup truck without compromising performance, based on a GMC Sierra 1500 vehicle.

Final engine assembly is penciled in to take place in the first quarter of 2016.

The engine uses a new cooled supercharger, Eaton’s VVA technology which was introduced on 2.5-litre GM four-cylinder engines in MY 2014. In the Envera engine, late intake valve closing is used to achieve the Atkinson cycle. And analysis by Eaton of its VVA mechanism suggests the Envera cam settings for efficiency, power and torque are attainable with the Eaton VVA mechanism.

Envera describes the VCR engine as “supercharged to attain 360 bhp (268kW) and V8-like driving responsiveness”. It is supercharged through a clutch

Envera puts forward two versions of its variable compression ratio design – VCR 1.0 and VCR 2.0. In VCR 1.0 the crankshaft is mounted in a ‘crankshaft cradle’ with the crankshaft axis and cradle axis offset by 13.5mm.

Pivoting the cradle 32 degrees varies the compression ratio from 8.5 to 18.6 to 1 according to Envera claims.

In the VCR 2.0 version, the research team puts forward the notion of a pre-assembled control shaft that slides in bearing sockets formed in the crankcase and what Envera calls a “cylinder jug”. Each cylinder gives the appearance of being a “jug” with the pre-assembled control shaft passing through the “handle” of the “jug”.

The control shaft is assembled by press fitting a steel eccentric onto the steel shaft, followed by sliding on an eccentric bronze bushing which is followed by another steel eccentric until the camshaft is fully assembled.

Envera proposes making the cylinder block of CGI material and mounting this in an aluminium crankcase.

Envera says: “CGI gives more robust cylinder walls and deck than stock aluminium crankcase with steel liners”.

The researchers claim the entire VCR 2.0 engine uses a stock cylinder head with Eaton VVL and Atkinson cycle cams, a nitrile curtain bonded to steel flanges giving a bond that os stronger than the curtain, and finally a stock bedplate and crankshaft for the bottom end of the engine.

Envera claims the VCR mechanism does not add mass to the cranktrain. High engine speeds and loads are allegedly attainable with conventional and reliable cranktrain technology.

Whether anything will come of the research programme remains to be seen, as OEMs appear reluctant to add too much complex (and costly) technology to their gasoline engines to gain extra performance. But Eaton is likely to gain mileage, possibly from the cooled supercharger (it is cooled by air from the intercooler) which uses an Eaton TVS 1320 rotor set. Envera claims that “with the new cooling technology, the supercharger can deliver higher pressures without overheating”.

Of course, the situation can be viewed from the other end of the telescope: because of the higher pressures generated, the supercharger needs to be cooled!

Whatever, GTPower power modelling points to projected values for the engine: 234g/kWh fuel economy; 440Nm torque at 2,500 rev/min, and 118kW/litre at 6,000 rev/min. All of this while with a 200kW/litre load capacity and a “near-stock engine length”.

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