Design of Affordable Multi-Cylinder Variable Compression Ratio (VCR) Engine for Advanced Combustion Research Purposes 2012-01-0414

The legislative limitations of vehicle exhaust emission together with the current and prospective growth of road transportation intensity calls for continuous effort to improve vehicle powertrains that must be done both in design and technology domains. As the powerful remedy, a new generation of combustion engines fitted with the variable compression ratio (VCR) feature is considered. VCR technology can extend the range of clean engine operations such as HCCI or other advanced combustion strategies, enabling reduction of all exhaust harmful compounds simultaneously.

There are several known technologies for performing variable compression ratio in combustion engines; some of them have been successfully tested in engine research rigs and/or vehicle prototypes. In the paper the proposal of application of variable compression ratio technology in four-cylinder, water-cooled engine is presented. In this project, the change of combustion chamber volume is the result of shifting the cylinder block - cylinder head assembly perpendicularly to the crankshaft axis. In consequence, compression ratio can be varied from 1:19 to 1:9. Despite of certain technical difficulties and practical feasibility, this design has specific advantages, but drawbacks too; they are shortly discussed as against the other known VCR solutions. The great benefit of presented design is its affordability due to limited costs and machining effort needed. The stock engine as a convertible base and available aftermarket engine components are widely used in the project. Although such approach may not aspire to mass-production applications, yet it makes possible to develop an advanced research tool and can be treated as the kind of low-budgetary alternative allowing sophisticated studies. Design layout of the engine as a whole, the shifting mechanism and necessary modifications in valvetrain system are shown in the paper.