Varying the timing of intake-valve closing was examined on a single-cylinder engine as a means for controlling the load of a homogeneous-charge spark-ignition engine. The engine was operated unthrottled, with load control obtained by holding the intake valve open during a portion of the compression stroke. This allowed the piston to push part of the cylinder charge back into the intake manifold. Comparisons to a conventional engine showed the late intake-valve-closing engine to have (1) lower pumping losses, (2) lower specific fuel consumption, (3) lower nitric oxide emissions, and (4) similar HC emissions. However, the fuel-economy benefit offered by this load-control concept would be reduced by the frictional losses of a control mechanism. The current trend toward lower vehicular power/weight ratios also would diminish the impetus for this approach.

Controlling engine load by means of late intake-valve closing

A Review and Classification of Variable Valve Timing Mechanisms

A Review of Variable Valve Timing Benefits and Modes of Operation

The efficiency of a vehicle having a body and a reciprocating piston four-stroke internal combustion engine is increased substantially by greatly reducing the size of the engine relative to the weight of the body. The great reduction in engine size relative to the weight of the body causes the engine to operate in a much more efficient range during almost all of the time of its operation. Peak power needs are satisfied by turbocharging and varying the compression ratio.

High efficiency vehicle and engine

The effect of bore-to-stroke (B/S) ratio on indicated specific fuel consumption (ISFC) and emissions of a gasoline-fueled, spark-ignited, single-cylinder engine was studied while holding compression ratio and bore diameter constant. From the baseline B/S of 1.1, B/S was increased to 2.2 and 3.3 by shortening the stroke length. The top dead center (TDC) piston position was raised with increasing B/S, since clearance volume must be decreased with stroke for a constant compression ratio. Test results based on lean air/fuel ratios, a wide open throttle, and maximum brake torque spark advance showed that increased ISFC and hydrocarbon exhaust emissions were primary deterrents to operation at a larger B/S in screening tests of B/S ratios (1.1, 2.2, and 3.3) at a 16.5:1 air/fuel ratio and 1500 rpm. A study of combustion chamber variations at 1.1 and 2.2 B/S ratios, an 18:1 air/fuel ratio, and engine speeds from 750 to 3000 rpm showed that ISFC was about 18% higher at 2.2 B/S than at 1.1 B/S. Cylinder heat loss at a larger B/S, expressed as a percent of fuel energy, could be minimized by reducing the combustion chamber surface-to-volume ratio at TDC and by increasing engine speed. Combustion duration could be reduced at a large B/S by more compact chamber geometries, more centralized or dual ignition, and increased mixture motion. The hydrocarbon emission index increased with surface-to-volume (S/V) ratio, decreased with increased engine speed, and was relatively independent of combustion duration. The nitric oxide emission index decreased with increased S/V ratio and decreased with increased combustion duration. The carbon monoxide emission index was relatively independent of S/V ratio, decreased with increased engine speed, and increased with combustion duration.

Engine combustion at large bore-to-stroke ratios

A five-cylinder variable displacement research engine has been designed, built, and tested for over one year. Displacement is varied by changing the piston stroke using a four-bar linkage. By proper choice of the linkage dimensions, compression ratio can be held constant as the stroke changes, or it can be tailored to optimize economy and performance. Before the engine was built, its dynamics were thoroughly analyzed, and a five-cylinder configuration was selected to minimize vibration. Test data show that BSFC is, as expected, less dependent on load than in conventional engines, and averages less than 0.5 lb/bhp-hr over the load and speed range of ordinary automobile operation. Several methods for estimating urban fuel economy from dynamometer data predict a significant improvement compared with conventional engines. Emission controls have not yet been applied to this engine.

A Variable-Displacement Spark-Ignition Engine

A five-cylinder variable displacement research engine was designed, built, and tested. Displacement is varied by changing the piston stroke using a four-bar linkage. Before the engine was built, its dynamics were thoroughly analyzed, and a five-cylinder configuration was selected to minimize vibration. Test data show that BSFC is, as expected, less dependent on load than in conventional engines, and averages less than 0.5 lb/bhp-hr over the load and speed range of ordinary automobile operation. The impact of exhaust gas recirculation on emissions levels was studied experimentally. Several methods for estimating urban fuel economy from dynamometer data predict a 20 to 25% improvement compared with conventional engines at the same emissions levels. (ERA citation 03:044973)

W. R. Delameter

Papers

A Variable-Displacement Spark-Ignition Engine

Variable-displacement spark-ignition engine. final report