An Advanced Turbocharging System for Improved Fuel Efficiency

Abstract

Turbochargers provide an efficient method of utilizing exhaust energy to boost intake air pressure for improved engine performance and efficiency. However transient operation requires increased air delivery (via quicker compressor response) to allow more rapid fueling for acceleration in both diesel and natural gas engines. In diesel engines rapid boosting will avoid increased particulates caused by excessive fueling during acceleration. Further, in applications that use either a wastegate, inlet bypass or variable vanes in the turbine to limit boost pressures, the excess energy in the exhaust is thrown away. The SuperTurbo™ (or superturbocharger) can recover much of the wasted energy and return it to the crankshaft, increasing overall efficiency. Woodward has developed a mechanical geartrain connected to the turbine shaft that transmits power through a variable speed hydraulic transmission to the crankshaft of an engine. This combination, a superturbocharger, provides the needed characteristics of (a) recovery of energy at high speed/load operating points (turbocompounding), (b) very rapid acceleration of the turbine shaft during transients (supercharging), (c) elimination of boost limitation devices, and (d) a variable speed hydraulic transmission that will be lower cost than a high-speed, high-power electrical system. While the air requirements are different for diesel and natural gas engines, both have sufficient exhaust energy to drive a turbine beyond the needs of the compressor for much of the performance map. Part load operation may be different as natural gas engines are usually throttled. The choice of a diesel or natural gas application was influenced by the availability of a suitable engine. The first prototype superturbocharger was built and tested on a Mack E7G natural gas engine, replacing the wastegated turbocharger of the stock engine. Preliminary results show fuel economy improvements of almost 6% at high speeds and high loads. In addition the load response of the engine was greatly increased due to the ability to accelerate turbine shaft speed, increasing boost. However there was a peak power output drop due to limitations in boost and imperfect sizing.

Key findings

• ▸The SuperTurbo system can recover much of the wasted energy in the exhaust and return it to the crankshaft.
• ▸The system provides rapid acceleration of the turbine shaft during transients, improving engine performance.
• ▸The SuperTurbo system can eliminate the need for wastegates, inlet bypasses, or variable vanes in the turbine.

Keywords

Identifiers

DOI

10.1115/icef2007-1808

Journal

ASME 2007 Internal Combustion Engine Division Fall Technical Conference

Year

2006