Diesel engines are widely used in commercial and military vehicles, as well as some light duty vehicles. The compression ratio is a compromise between power, economy, and cold startability. The optimum ratio for economy is near 14:1 to 15:1, whereas the necessary compression ratio for cold starting ranges from 16 to 22:1 depending on the specific design of the engine and its application. This is too high for best economy and optimum boost. The proposal objective is to demonstrate a simple mechanism to vary the compression ratio between high (for cold starting) and low (for warmed-up running). This is accomplished during engine starting by causing the intake valve to close early (at bottom center), providing up to three ratios additional compression. Our plan is to reconfigure the valve mechanism to provide the desired function. Once running, the cam operates the valve normally. Minimal or no engine block modifications are anticipated. The work proposed is to develop the reconfigured valve mechanism and demonstrate its viability in a bench test rig with appropriate control strategy. For the SBIR OPTION, a system will be installed on one cylinder of a multi-cylinder engine and motoring tests run to demonstrate effectiveness.
Benefit: A review of the technical literature suggests that with the lower compression ratio, Diesel fuel economy would be improved by up to 12%, a significant step towards energy independence. Moreover, the literature suggests that both smoke and NOx emissions would be reduced at the lower compression ratio. Because the change primarily involves the valve train parts, implementation could occur quickly. For older engines, the compression ratio would have to be lowered (probably by modest redesign of the piston bowl) in order to realize the economy benefit. Specific engine models could be modified fairly quickly; whereas others might require more effort; or not be amenable to such a change. This technology could be combined with other technologies in an attempt to reach the DoD target of 40% to 60% fuel economy gains.
Keywords: Variable, Variable, Engine, Compression, ratio, VALVE, Actuation, efficiency
