Thermodynamic Systems for Tier 2 Bin 2 Diesel Engines

Light duty vehicle emission standards are getting more stringent than ever before as stipulated by US EPA Tier 2 Standards and LEV III regulations proposed by CARB. The research in this paper sponsored by US DoE is focused towards developing a Tier 2 Bin 2 Emissions compliant light duty pickup truck with class leading fuel economy targets of 22.4 mpg “City” / 34.3 mpg “Highway”. Many advanced technologies comprising both engine and after-treatment systems are essential towards accomplishing this goal. The objective of this paper would be to discuss key engine technology enablers that will help in achieving the target emission levels and fuel economy. Several enabling technologies comprising air-handling, fuel system and base engine design requirements will be discussed in this paper highlighting both experimental and analytical evaluations. Mostly, this paper will focus on steady-state emissions and fuel consumption results that are tied to operating duty cycle with actual vehicle comparisons wherever applicable. GT-Power 1D cycle simulation analysis was done to narrow the turbocharger and air-handling architecture evaluation. The importance of turbocharger matching is critical to achieving both power density and emission goals. This paper highlights the challenges involved in selecting a single stage variable geometry turbocharger capable of delivering a 75hp/liter power density in addition to meeting light duty drive cycle emission requirements. The benefits of low pressure [LP] and high pressure [HP] EGR systems for this light-duty engine architecture will be explored in detail along with outlining the possible strategy of dual loop EGR to reduce overall fuel consumption.

On the combustion system development, this paper will highlight the importance of compression ratio, variable swirl architecture, injector nozzle hardware and injection strategy optimization towards meeting the stringent emissions, fuel consumption and noise targets. Fundamental thermodynamic explanations relating the fuel consumption improvements back to closed cycle and open cycle work are also being presented. Also, the paper will discuss challenges involving unburned HC and CO emissions when operating in premixed/low temperature combustion like regimes involving higher EGR rates and early pilot injection timings. Potential solutions to mitigate such undesired emissions have been investigated both analytically and experimentally.