2/4SIGHT engine concept switches between 2 and 4 stroke operation

Until electric cars and their associated technologies (motors, batteries, controllers etc.) become mainstream, the internal combustion engine will need to be further refined in order to meet upcoming fuel economy requirements and current emissions regulations -- while still producing the power that consumers have come to expect. HCCI is one technology currently being developed to make these goals possible, while direct injection and turbocharging are simply becoming quite common.

Ricardo has developed a new prototype engine called 2/4SIGHT which could give HCCI a run for its money. An engine equipped with this new system is capable of running on either the 2 or 4 stroke engine cycle, allowing their V6 test-bed to be downsized from 3.5 liters to 2.0 liters while making the same power output. This downsizing leads to a 27 percent reduction in fuel consumption and correspondingly lowered emissions.

Ricardo believes that their 2/4SIGHT technology will be cost effective and easy to package for vehicle use. A video of the test engine switching from 2 to 4 stroke can be seen here.

[Source: Ricardo]
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."