Business Green: Technology gurus turned venture capitalists Bill Gates and Vinod Khosla have invested a combined $23.5m in EcoMotors. This will enable the company to complete development and testing of its Opoc engine. Opoc — opposed piston, opposed cylinder — is essentially a two-stroke engine which is half the size and weight of a conventional internal combustion engine of comparable output and can thus achieve up to 50 per cent greater fuel efficiencies with commensurate emission reductions. It …