Search Results

Additive control of DIG injector coking was investigated on two dynamometer-operated engines and validated in a vehicle. The first engine was a Nissan research “mule” engine designed to severely coke the injectors so that additive effect could be more easily discriminated. Initial additive screening and optimization was carried out in this engine and a few chosen candidates of the Mannich chemistry-type were further optimized in the second engine, and in a vehicle. The second engine, which was also dynamometer operated, was an advanced wall-guided design capable of both homogeneous and stratified operation. On this engine we were able to optimize the Mannich additive “Man C-2” separately in two different carrier systems to show a carrier effect, and by manipulating the purity of the base detergent Man C-2 to show a detergent activity modulation by trace co-products.

Throughout the world, governments are promulgating regulations that are intended to improve air quality. Some of these regulations affect the physical and chemical properties of gasoline. Consequently, refiners are under increasing pressure to reformulate their gasoline to be lower emitting when handled and combusted. These regulatory actions have also greatly reduced flexibility in the fuel formulation process. In many cases, refiners are attempting to reduce gasoline vapor pressure, sulfur, aromatic, and olefin content while simultaneously tightening distillation characteristics by removing butane and reducing the use of heavy reformate and FCC fractions. Because butane, aromatics and olefins can contribute substantially to pool octane levels, blending clean-burning gasoline with the required octane rating for acceptable vehicle performance can be difficult.

SAE Paper 2002-01-2894 entitled, “The Impact of MMT Gasoline Additive on Exhaust Emissions and Fuel Economy of Low Emission Vehicles (LEV)” presents discussion and conclusions concerning the emissions from vehicles that accumulated mileage on gasoline with and without the fuel additive, methylcyclopentadienyl manganese tricarbonyl (or MMT®). Although the authors of the paper express concern about use of MMT®, the data on which the authors rely are consistent with the results and conclusions from prior evaluations of MMT® which have found that MMT® is compatible with effective emission control system operation (1,2,3). All vehicles tested in the study met the emission standards for all pollutants that apply to the test vehicles in-use and analysis of the data show MMT® had no effect on fuel economy.

This paper presents the findings of some fundamental characterisation of the deposits that form on the injectors of an air-assisted DISI automotive engine, including the effect of these deposits on engine performance when operated in different combustion modes, with varying fuel composition and additive content. A root cause analysis was undertaken, including an assessment of injector temperature and deposit chemistry. Fuels from a matrix designed around the European year 2000 gasoline specifications for T90, olefin and aromatic levels were used to study the effect of fuel composition on deposit formation. Two commercial gasoline detergent additives, of different chemistries, were used to investigate the impact on deposit formation. The results of the fuels study and deposit analysis are consistent with published theories concerning fuel composition impact on combustion chamber deposit (CCD).

The long-term durability of a vehicle's exhaust catalyst is essential for emission control. Catalyst durability can be affected by a variety of factors including engine oil consumption. During normal engine operation, some of the lubricating oil is combusted. The deposition of combustion products from phosphorus containing lubricant additives on the catalyst can adversely affect catalyst durability. In an attempt to minimize the impact of oil consumption on additive performance, engines have been designed to reduce oil consumption and oils are being formulated with lower concentrations of phosphorus compounds. However, these phosphorus compounds protect the engine from excessive wear and cannot be easily removed from lubricant oil due to concerns over engine durability. The use of a phosphorus scavenger is an approach that works together with engine design to minimize catalyst deterioration.

The effects of fuel composition and engine operating parameters on high-pressure, direct injection gasoline (DIG) injector plugging and deposit formation have been studied. The engine used was a conventional dual-sparkplug, 2.2-liter Nissan engine modified for direct injection using one of the spark plug holes. The engine was run under 20% rich conditions to accelerate deposit formation. A ten-fuel test matrix was designed around T90, sulfur level, and olefin levels indicated in the European gasoline specifications for year 2000. The gasolines, containing no detergents, were formulated using refinery stream blends to match the specified targets. Injector flow loss was monitored by fuel flow to the engine and monitoring oxygen sensors on each of the four cylinders. The impact of fuel composition on deposit formation and injector plugging is discussed. Injector flow loss was strongly influenced by injector tip temperature.

The Clean Air Act of 1990 requires on-board diagnostics (OED) capabilities on all new vehicles. These diagnostic systems monitor the performance of engine and emission system components and inform the vehicle operator when component or system degradation could significantly impact emissions. Acceptable operation of the monitor requires proper treatment of system variables. Fuel composition is one of many possible variables that must be considered for monitoring components directly in the exhaust stream. Recently, the octane enhancing, emissions reducing additive methylcyclopentadienyl manganese tricarbonyl (MMT) was reintroduced into unleaded gasoline in the U.S. Prior to reintroduction, the additive underwent extensive testing to demonstrate that use of MMT does not adversely affect vehicle emissions or the operation of emission systems such as OBD. However, questions have been raised about the influence of the additive on OBD systems.

MMT (methylcyclopentadienyl manganese tricarbonyl) is an antiknock additive for unleaded gasoline, which is now required for cars equipped with catalytic converters. Because of its effectiveness, MMT is economically attractive compared with achieving antiknock quality by refinery processing. Use of MMT in gasoline at a concentration of 0.125 g of contained manganese per gallon provides, on the average, about 2 road octane numbers. Compared to processing, this could represent a savings in crude oil of about 1%. Like other antiknocks, the economic attractiveness of MMT is greatest at low concentrations. Extensive road and dynamometer engine tests have shown that use of MMT in the recommended concentration range is compatible with general aspects of car operation--octane number requirement, exhaust valve and spark plug durability, and exhaust gas recycle for NOx control. Moreover, beneficial effects in exhaust valve guide and seat wear have been observed with MMT in some tests.

This paper presents the results of an investigation cooperatively undertaken by Esso Research and Engineering Company and Ethyl Corporation to determine whether the hydrocarbon-type effect observed in road antiknock studies of gasolines is independent of other fuel properties over and above laboratory octane numbers. For this study, 51 finished gasolines were carefully blended from 57 base stock components to provide controlled levels of those major fuel properties which affect road performance. The controlled properties were Research octane number, sensitivity (RON minus MON), ratio of aromatics to olefins, tetraethyllead content, octane-number distribution in the fuel's boiling range, boiling-range location of the unsaturated hydrocarbons, and sulfur content. A unique feature of the blending scheme was the formulation of blend pairs, in which all but one of the major fuel properties were essentially equal.

Two gasolines may have the same Research octane number, the same Motor octane number, and the same over-all hydrocarbon composition yet differ significantly in road antiknock performance. This paper concludes that such variation can be related to the placement of hydrocarbon types in the boiling range of the gasolines. Specifically, studies show that the low-boiling olefins provided better road performance than did the high-boiling olefins. Also, low-boiling aromatics gave better road ratings than the high-boiling aromatics. The magnitude of these effects varied with vehicle engine speed. For this study, twenty fuels of nominal 100 Research octane number were designed on a statistical basis. Realistic gasoline components were used. Comprehensive laboratory inspections of the fuels and fractions included more than 700 laboratory antiknock ratings, 400 hydrocarbon type analyses, and complete volatility data.