Present Day Spark-Ignition Engine Pollutant Emissions: Proposed Model for Refinery Bases Impact 2001-01-3529

Air quality improvement, especially in urban areas, is one of the major concerns for the coming years. For this reason, car manufacturers, equipment manufacturers and refiners have explored development issues to comply with increasingly severe anti-pollution requirements. In such a context, the identification of the most promising improvement options is essential.

A research program, carried out by IFP (Institut Français du Pétrole), and supported by the French Ministry of Industry, IFP, PSA-Peugeot-Citroën, Renault and RVI (Renault Véhicules Industriels), has been built to study this point. It is based on a three years program with different steps focused on new engine technologies which will be available in the next 20 years in order to answer to more and more severe pollutant and CO₂ emission regulations. This program is divided into three main parts: the first one for Diesel car engines, the second for Diesel truck engines and the third for spark ignition engines.

The work reported here takes place in the spark-ignition section of this research. Its aim is to characterize the effect of fuel formulation on pollutant emissions and engine tuning for different spark ignition passenger cars. The originality of this study is to use refinery bases as parameters and not conventional parameters: the tested fuels have been chosen in order to represent the major refinery bases expected to be produced in the near future. These results, expressed with linear correlations between fuel composition and pollutant emissions, will help to give a new orientation to refinery tool.

The two engines presented in this paper are a Euro2 lean-burn engine (Honda VTEC which equips the Honda Civic) and a Euro3 1.8 liters stoichiometric-running Renault engine which equips the Laguna vehicles. On each engine, tests have been made on a steady state bench with variations of some running parameters such as A/F ratio, spark timing or EGR rate. Vehicle tests with the same engines have also been done: on a European MVEG cycle, regulated and unregulated pollutant emissions have been recorded.

Fuel composition in terms of refinery base composition has a strong influence on engines emissions and running. Some effects are common to both engines, but differences can be outlined, linked with distinct running conditions.

• Reformates increase HC emissions for both engines.
• NOx, HC and CO emissions are closely linked and most of the effects of bases on NOx can be explained by partial burn, especially for Dimate and ETBE.
• The behavior of ETBE has been particularly studied in order to explain the differences induced by the engine type and the running parameters (A/F ratio, EGR rate, etc.) on the contribution of this base.
• Non regulated pollutant (speciated hydrocarbons, oxygenated compounds) composition is directly linked with fuel composition and mechanisms of formation for some of them have been proposed.

The conclusions of this research study will aid the judicious choice of refinery components to reduce diesel vehicle emissions.