Modern Diesel Engine Performance Potential with the Lowest Raw Emissions

The modern DI diesel engine, within the last couple of decades, has proven to be an economical and attractive alternative in the modern passenger car segment. This is attributable to its higher process efficiency and torque characteristics. The recent rise in consumer acceptance of the DI diesel engine is a result of improved drivability and acoustics, which has contributed to the reduction of fleet fuel consumption as a part of the ACEA voluntary commitment. This has been achieved by maintaining the diesel engine's traditionally low fuel consumption, while also fulfilling strict emission regulations. The combination of recent indications of climate change that are linked to the use of fossil fuels and rising fuel prices, has brought fuel consumption into the limelight for the entire spectrum of manufacturers and their development teams.

To meet the continuously increasing demands that result from this situation, the combustion system also needs to be redesigned. This measure is necessary, so that the disadvantages of exhaust aftertreatment systems (for example, DPF) can be minimized through significantly reduced engine-out emissions, which increases fuel efficiency. FEV analyzed all of the design parameters of the diesel combustion system in detail and evaluated them for future demands. FEV's High Efficiency Combustion System (HECS) became the solution, which is designed and tailored for high EGR tolerance and combines low nitrogen oxide emissions with superior fuel efficiency, even under high part load conditions.

The following aspects are the primary elements of this optimized combustion system layout:

• Optimization of mixture formation (fuel injection and swirl)
• Improved cylinder filling with optimized gas exchange (boosting, manifold layout and flow losses)
• Highly capable boosting system, in conjunction with a combined high pressure and low pressure EGR system
• Adjustment of the combustion chamber (geometry and compression ratio) to the air and fuel system capabilities
• Intensified cooling (Air and EGR)
• Implementation of a high-performance glow plug system

The careful layout of the combustion chamber geometry, with the aid of modern CFD tools, ensures an ideal air utilization even within the nominal speed range. Air-fuel ratios of nearly 1.1 are realized at engine speeds above 3500 rpm, which provide proof of the significant improvement over the state-of-art. In comparison to the larger base engine, an improvement in low-end torque is possible through the combination of carefully laid out process parameters, such as charge motion, spray pattern and piston bowl shape. In addition, flexible multiple injection and two-stage turbocharging also improve low-end torque, in spite of the reduction in engine capacity. Improving the gas exchange and significantly lowering charge temperatures leads to a shift toward leaner air-fuel ratios. This consequently results in substantially increased EGR rates, which permit a major reduction in untreated emissions.

The improved NOx / BSFC trade-off can then be targeted separately from an improvement in the NOx / PM trade-off

The lowest possible NOx emissions can be obtained through the integration of a new, model-based control concept and the subsequent linking of these structures to innovative approaches that control combustion.  This is accomplished with the help of an integrated pressure sensor and glow plug, allowing a near ideal configuration of combustion parameters. In addition, the considerably improved PM emissions guarantee longer regeneration intervals for the DPF, contributing to a further increase in fuel efficiency for everyday operation.

These improvements could be combined with developments in other areas, for the purpose of providing a complete analysis of the potential of diesel drivetrains. Therefore, the following aspects are of particular interest in the continual development of diesel engine technology:

• Optimization of the mechanics and reduction in friction losses
• Hybrid development (start / stop, regeneration, power boost function)
• Vehicle improvements (weight, air and rolling resistance)
• Drivetrain optimization (gearbox and transmission ratio losses)

The HECS concept, in conjunction with the other technology concepts that are mentioned, could realize a 40% reduction in fuel consumption for a mid-sized car (vehicle class: 1590 kg / 3500 lbs.) and result in equal driving comfort or possibly even provide an improvement.

We are working on a variety of diesel engine projects to further increase fuel efficiency and decrease emissions, in order to facilitate the customer’s individual mobility. Apart from innovative concept vehicles and demonstrator vehicles, we are also working on a variety of production development programs for the global automotive market. We look forward to assisting you in achieving your goals.

Emission Performance and Efficiency of the HECS Engine (Part Load Point @ ~2300 rpm)