Increased Internal Combustion Engine Efficiency with Optimized Valve Timings in Extended Stroke Operation

Abstract

Spark-ignited internal combustion engines are known to exhibit a decreased brake efficiency in part-load operation. Similarly to cylinder deactivation, the x-stroke operation presented in this paper is an adjustable form of skip-cycle operation. It is an effective measure to increase the efficiency of an internal combustion engine, which has to be equipped with a variable valve train to enable this feature. This paper presents an optimization procedure for the exhaust valve timings applicable to any valid stroke operation number greater than four. In the first part, the gas spring operation, during which all gas exchange valves are closed, is explained, as well as how it affects the indicated efficiency and the blow-by mass flow. In the second part, a simulation model with variable valve timings, parameterized with measurement data obtained on the engine test, is used to find the optimal valve timings. We show that in 12-stroke operation and with a cylinder load of 5 Nm, an indicated efficiency of 34.3% is achieved. Preloading the gas spring with residual gas prevents oil suction and thus helps to reduce hydrocarbon emissions. Measurements of load variations in 4-, 8-, and 12-stroke operations show that by applying an x-stroke operation, the indicated efficiency remains high and the center of combustion remains optimal in the range of significantly lower torque outputs.

Optimal Degree of Hybridization for Spark-Ignited Engines with Optional Variable Valve Timings

“…The models of the internal combustion engines are based on data obtained from measurements on engine test benches. The brake efficiency improvement by up to 40% by dethrottling and an x-stroke operation has been verified by an internally developed fully variable valve train that was published in [45].…”

“…By applying Miller valve timings to achieve the desired engine load instead of adjusting the conventional throttle, the efficiency of the part-load operation is improved [44]. Furthermore, with a cylinder-deactivation mode and the implementation of an x-stroke operation, where the usual four strokes of the engine are extended up to 'x' strokes, the efficiency of very low engine loads is increased significantly [45]. To solve the optimization task, we apply dynamic programming (DP), which leads to a noncausal but globally optimal operating strategy [46].…”

“…The turbocharged engine is modeled with own data obtained from measurements on an engine test bench equipped with a 3.0 L direct-injected SI engine. The increase of the indicated efficiency in part-load operation due to an FVVT is additionally quantified on an engine test bench with a four-cylinder 1.4 L SI engine equipped with an internally developed FVVT [45]. All results are expressed in units that allow a comparison of engines with different displacement volumes [55].…”

“…For the engine with the camshaft as well as for the engine with the FVVT, the pumping losses decrease linearly to a minimum of approximately 0.05 bar as the load increases. Second, an FVVT enables the engine to run part-load operating points in an x-stroke operation or with deactivated cylinders, which significantly increases the indicated efficiency as shown in [45]. The lines colored represent NA engines with a maximal value of p mi of approximately 12.5 bar while the black lines represent TC engines with a maximal p mi of approximately 22 bar.…”

Increase in the Fuel Efficiency of a Diesel Engine by Disconnecting Some of Its Cylinders

“…The works of scientists [10][11][12][13][14][15] deal with complex issues of a more complete additional loading of the cylinders remaining in operation, a decrease in specific and liter fuel consumption, and an increase in fuel efficiency.…”