Ricardo Cracks Barrier Between Two- And Four-Cycle Engines

Motorheads have been dreaming about an electromagnetic valve train for years now. A virtual cam profile, in concert with the elimination of floating valves, opens up endless possibilities for engine tuning. The dream is inching closer to reality, as power electronics shrink and the manufacture of rare-earth magnets gets continually better. A closed-loop valve system could be here sooner rather later (I know, I know, but please contain your urge to drool). In fact, Ricardo engineering seems to be breaking down the boundaries of existing technology, as they claim to have developed a blended two- and four-cycle power plant.

Without real technical details, it's virtually impossible to dissect the actual electro-mechanical layout of this concept, but we have some speculation as to how it might work. Traditionally, the problem of a running a four-cycle in the same manner as a two-cycle has been how to get the exhaust out. This is partially solved in the Miller cycle, when the intake valves are opened after the exhaust stroke and some form of compression pushes remaining exhaust out with fresh air. In a two-cycle engine, the valving is designed to take advantage of both the up and down stroke of the motor to push exhaust and fresh air through the combustion chamber. This is an inherently dirty—but extremely powerful—system, because a power stroke occurs twice as often as a four-cycle engine.

Ricardo says that it's using electromagnetic valves, which can operate completely independently of each other and the piston based on software running power electronics. Direct injection and a Honeywell turbo blend the two different cycles together. We suspect the system looks like a normal engine, minus the hole in the side of the cylinder liner necessary in a normal two-cycle. It starts up like a normal engine, but on demand can double the cylinder fire frequency and utilize a Miller cycle-like strategy to evacuate gas from the compression chamber.

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This is all speculation, but the engine geek in us is very excited to see where the internal combustion engine can be taken one electromagnetic valves are reliable (and don't destroy valve seats). Imagine having a lumpy, long-duration cam profile—Heck, apparently even a 2 cycle engine!—for acceleration, and then a lean-mean mileage cam for over the road travel. Brilliant! And it's not magic, it's engineering.

27% fuel savings projected as 2/4-stroke research prototype engine completes initial testing

Ricardo and a consortium of automotive partners today announced the
completion of an advanced prototype research programme based on the
highly innovative 2/4SIGHT engine concept. This gasoline engine
concept uses novel combustion, boosting, control and valve actuation
technologies to enable automatic and seamless switching between two-
and four-stroke operation, with the aim of delivering significant
performance and fuel economy improvements through aggressive downsizing

The 2/4SIGHT engine concept uses a direct injection gasoline
combustion system in which the design of intake and exhaust ports,
combined with appropriate changes in boost supply, fuel injection,
ignition and valve timing, enable operation both in two-stroke and
four-stroke modes. An advanced control system coupled with flexible
valve actuation manages driver demands and coordinates operation of
the boost system, valves and fuel injection equipment at an individual
cylinder level. This enables smooth transitions between two- and four-
stroke operation without torque interruption in both transient and
constant torque conditions.

Prototype engine configuration
The research prototype engine is based on a single bank of a 2.1 litre
V6, which in 6 cylinder 2/4SIGHT configuration is intended to deliver
levels of performance and driveability more usually associated with a
3-4 litre V8 gasoline engine. In order to enable the project team to
assess control strategies in a completely unrestricted manner, an
electro-hydraulic valve (EHV) actuation system was used for the
prototype development rig. The air handling system of the 2/4SIGHT
concept is based on two-stage boosting and intercooling using a Rotrex
supercharger and Honeywell turbocharger. For simplicity in the initial
test bed prototype configuration however, boosting is provided by an
external compressed air supply. The engine control system of the
prototype is a DENSO rapid prototyping system working with DENSO
gasoline direct injection and ignition components. The prototype
engine was built at the Ricardo Shoreham Technical Centre and
installed for testing at the Sir Harry Ricardo Laboratories of the
University of Brighton.

Development test results
Testing of the prototype 2/4SIGHT engine has enabled development and
validation of the combustion system which has been optimised for
operation in both two and four-stroke modes. The flexibility of the
advanced control system - developed jointly by DENSO and Ricardo -
allows rapid changes to high level code which, coupled with the
flexibility of the EHV valvetrain, has enabled the project team to
develop and optimise a new control strategy for the 2/4SIGHT engine,
including the management of two-four-stroke switching.

Highlights of the development test results include:

* Smooth and reliable switching between two- and four-stroke
modes under both constant torque conditions and transient operation.
* Control strategies amenable to implementation in cost-effective
mechanical valvetrain hardware.
* Extremely high two-stroke specific torque demonstrated of 150
Nm/L at 1000 rev/min and 230 Nm/L at 2500 rev/min, opening the
prospect of highly aggressive engine downsizing using the 2/4SIGHT
engine concept.

Significant improvements in fuel economy
Following completion of the test programme, Ricardo has carried out a
vehicle drive cycle and acceleration performance simulation based on
the steady state fuel consumption and full load performance of the
2/4SIGHT engine. The study was carried out using the Ricardo
powertrain blockset in the MSC "EASY5™" software package that allows
detailed modelling of engines, transmissions, drivelines, tyres and
aerodynamics. The baseline vehicle for the study was an 1800 kg
passenger car sold in the European market with a 3.5 litre naturally
aspirated V6 gasoline engine and 5 speed conventional automatic
transmission with torque converter. To verify the validity of the
models and input data, the baseline vehicle fuel consumption results
were compared with published data, which were reproduced by the model
to an acceptable accuracy of 1%.

The simulation results indicate that vehicle acceleration performance,
including launch from rest, can be maintained with a 2.0 litre V6
2/4SIGHT gasoline engine replacing the 3.5 litre baseline powerplant.
This would deliver fuel savings of 27% over the New European Drive
Cycle (NEDC) and would reduce the vehicle CO2 emissions of the
baseline from 260 g/km to 190 g/km.

Excellent cost-benefit trade-off
In parallel with the prototype engine development effort in the UK,
Ricardo engineers at the company's Detroit Technology Campus have
designed a patented mechanical cam switching system which is capable
of delivering the required switching performance for the control
strategies developed on the test bed using the EHV system for the
2/4SIGHT engine. This not only opens the way for packaging and
integration of the 2/4SIGHT engine into a production vehicle but also
represents a highly cost-effective means of implementation of this
highly efficient combustion concept. As such a future gasoline engine
equipped with 2/4SIGHT technology offers the prospect of superior
performance and lower production cost than other advanced gasoline and
diesel powertrains, and straightforward compliance with gasoline
engine emissions standards.

Having completed development of the prototype 2/4SIGHT engine, the
partners are currently negotiating potential sources of funding and
support for a vehicle demonstration programme. Commenting on the
successful completion of the prototype engine development programme,
Ricardo technology director, Neville Jackson, said:

"The completion of the prototype engine development programme of the
2/4SIGHT engine and demonstration of its two-/four-stroke switching
capability is an important milestone for the project partners. While
significant further research and development challenges remain, not
least in the vehicle demonstration of this advanced engine concept,
the initial prototype development project has demonstrated the
potential of 2/4SIGHT to offer improved gasoline fuel economy and
reduced CO2 emissions, while also maintaining or improving vehicle
performance. In addition to validating the 2/4SIGHT concept, the
research project is also delivering significant benefits in terms of
its many constituent technologies which are likely to see application
in the more immediate term."

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