Optimizing a CNG-Fueled Spark Injection Engine for a Parallel Hybrid Powertrain

. Splash oil cooling was provided in the engine block to compensate for the increased introduction of heat into the piston crown, and to reduce NO_x emissions.

The high specific engine output, the splash-oil cooling and the turbocharger generated a significant increase in the introduction of heat into the engine oil; an additional oil-to-water heat exchanger was installed for this reason.

The cylinder head largely conforms to the base engine, with the exception of asymmetrically designed intake ports to support the high EGR rate while simultaneously reducing engine-out NO_x. One of the intake ports was designed as a swirl duct, the other as a fill duct. Compared with the standard cylinder head, it was possible to increase the swirl level in the combustion chamber.

Exhaust-gas turbocharging was selected to realize the highest levels of efficiency. The exhaust manifold and upstream catalytic converter was replaced by a manifold with a turbocharger flange. To utilize the exhaust-gas dynamics in a 3-cylinder engine, the cross sections (damping volumes) of the exhaust manifold were minimized. Boost pressure is controlled by a pulse-width-modulated activation of the overpressure actuated turbine bypass (waste gate).

Starting out from the original engine application (variant I) the carbon-dioxide emissions are lowered by 1.9% by the use of an oversize turbocharger (variant II). In combination with the Active-WG strategy (variant III) a further lowering by 1.0% is successful. The greatest reduction potential (4.5%) is provided by a combination of all the methods examined (variant IV). Here it was possible to lower the carbon-dioxide emissions below the requested 90 g/km in the NEDC.

—Boland et al.

Resources

• Daniel Boland et al. (2010) Optimization of a CNG Driven SI Engine Within a Parallel Hybrid Power Train by Using EGR and an Oversized Turbocharger with Active-WG Control (SAE 2010-01-0820)