New HCCI/CAI Combustion Process Development: Methodology for Determination of Relevant Fuel Parameters

N Jeuland,X Montagne

doi:10.2516/ogst:2006006x

Abstract

To pass the simultaneous emission requirements for near zero pollutant and for low CO2 , which are the challenges of future powertrains many research studies are currently carried out over the world on new engine combustion processes, such as the Controlled Auto-Ignition (CAITM ) for gasoline engines and the Homogeneous Charge Compression Ignition (HCCI) for diesel engines. These new processes have the potential to reduce, by a factor from 10 to 100, the NOx and articulate emissions (PM) in comparison with a typical gasoline or diesel engine. The main issue in the development of such combustion modes remains the limited range of engine speed and load that enable good engine running, according to required levels for NOx and noise emissions. One of the most promising ways to increase the CAI combustion range lies in the formulation of dedicated fuels, optimised to enhance combustion initiation by modifying and controlling the auto-ignition characteristics and/or the fuel physical and chemical properties. To select the fuels, a new procedure has been set-up that allows a better characterization of the fuel impact on engine running in CAI, for various conditions of speed and load. The use of this methodology for a large set of fuels, formulated according to their auto-ignition characteristics, volatility and chemical composition has underlined the complexity of the action of fuel and has enabled one to point out the most influent fuel characteristics to over as large as possible requirements.

Highlights

Fuels and engines used in road transportation have to face two main challenges in a highly competitive economy: – To reduce pollutant emission levels to such values that air quality in the cities complies with World Health Organization standards; – To reduce carbon dioxide emissions (CO2) which is regarded as the major greenhouse gas contributing to global warming and climate change
In order to face these two challenges, new combustion mode such as CAI (Controlled Auto-ignition) or HCCI (Homogeneous Charge Compression Ignition) can have an important potential, by strongly reducing the NOx emissions and being able to pass emission levels without important post-treatment systems, which often induce a high cost in terms of CO2 emissions ([1] to [12])
Among the parameters affecting the CAI range, one of the key issues for the CAI combustion process based on the use of a high rate of internal EGR is the precise control of the switch from the CAI mode to the classical SI one necessary at very low load and at high load

Summary

Introduction

Fuels and engines used in road transportation have to face two main challenges in a highly competitive economy: – To reduce pollutant emission levels to such values that air quality in the cities complies with World Health Organization standards; – To reduce carbon dioxide emissions (CO2) which is regarded as the major greenhouse gas contributing to global warming and climate change. Several companies have developed variable valve trains able to change valve timing from cycle-to-cycle [13, 14]. These systems could help to make more flexible the cycle to cycle combustion control and to extend the CAI application range, which is the other key issue of the concept. They remain, for the moment, rather complex, expensive and they induce a significant increase of engine parameter to control

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Conclusion