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Project Sabre: A Close-Spaced Direct Injection 3-Cylinder Engine with Synergistic Technologies to Achieve Low CO2 Output
Abstract:
The paper describes the design and development of ‘Sabre’, a 3-cylinder engine encompassing a combination of technologies to realise low CO2 in a practical automotive application while retaining driving pleasure (vehicle acceleration performance). This project is a partnership with Continental Automotive, in which Lotus Engineering is responsible for the base engine and combustion system.
The decision process that led to a close-spaced direct injection combustion system that does not target high BMEP as the chief route to low fuel consumption is described. Instead of pursuing an approach in which specific power is maximized in order to reduce throttling losses at part load, mild downsizing coupled with throttling loss reduction and turbulence manipulation enabled by a switching valve train is employed. This approach, together with the use of an integrated exhaust manifold, enables cylinder head packaging benefits together with improved driveability and reduced high-load fuel consumption as a result of a lower boost requirement. The interaction of spray and air motion in the resulting homogeneous combustion system is briefly discussed.
The rationale behind the choice of a 3-cylinder layout is also discussed which, in addition to reducing friction and engine mass, also contributes towards knock control by removing blowdown pulse interaction between the cylinders. Friction reduction methods are discussed which centre around the use of laser-deposition bores and roller bearings on the balance shaft. The balance shaft helps to address the NVH issues expected from the layout, together with the very low CoV of IMEP afforded by the combustion process. The technology under-pinning the integrated exhaust manifold is also discussed. This simultaneously improves thermal management and reduces mass and bill-of-material (BOM) costs in this integrated engine concept.