FEV Inc., (FEV) a leading developer of advanced powertrain and vehicle technologies, will exhibit a lean burn engine concept at the SAE 2011 World Congress that has been modified to run on Compressed Natural Gas (CNG). The engine is designed for use in light-duty vehicles, and demonstrates the potential of modifying passenger vehicle engines to achieve diesel-like fuel efficiency and power using CNG as an alternative fuel.
The Advanced Turbulence Assisted Combustion (ATAC) system was implemented via modifications to the cylinder head, combustion chamber, pistons and intake system to create high turbulence through an increase in the intake swirl from the baseline diesel engine. FEV developed ATAC more than a decade ago, targeting large-bore engines in stationary and heavy-duty applications.
The lean burn combustion process also offers significant improvements in fuel consumption and CO2 emissions in comparison with more conventional CNG technology as a result of dethrottling and better combustion efficiency.
The effects of our dependency on a petroleum-based infrastructure have recently been demonstrated on the global stage as we see fuel prices rise and automotive market capitalization decline. t is a wake-up call that we must develop the technology that can run on alternative fuel sources that are available both cost effectively and domestically. This engine demonstrates a potential near-term solution.—Gary Rogers, FEV, Inc. president and CEO
Natural gas offers significant benefits in comparison with conventional fossil fuels, due to inherently better lean burn combustion properties and reduced knocking tendency, as well as better mixture preparation characteristics. A diesel engine has been selected as the baseline for the development to enable the benefits of combustion at high peak pressures.
In developing the demonstrator, FEV implemented a number of alterations to a Volkswagen 2L TDI base engine design, including creating a custom intake manifold, requiring the modification of the direct injection system, creating a multi-point injection system similar to port injection. FEV also optimized the velocity of the charge entering the combustion chamber, the piston geometry, the type of spark plug (whether for stoichiometric or lean burn), and made necessary adjustments to the turbocharger.
The compression ratio is adjusted so that it falls between a diesel and a gasoline engine compression ratio, resulting in higher combustion efficiencies.
In addition to the design of new components, FEV considered the increased strain on various components, such as valves and valve seats. Due to the operating conditions characteristic for CNG combustion, parts were designed to be more robust to mitigate excessive wear.
M. Umierski, Th. Körfer, P. Stommel (1999) Low Emission and Fuel Consumption Natural Gas Engines with High Power Density for Stationary and Heavy-Duty Application (SAE 1999-01-2896)
M. Umierski, P. Stommel (2000) Fuel Efficient Natural Gas Engine with Common-Rail Micro-Pilot Injection (SAE 2000-01-3080)