SAE 972841. Fuel and Additive ..... 400, Atlanta, GA 30346, U.S.A.. 6. "AAMA gasoline ... and their effects in a spark-ignition engine", SAE Paper. No.950680 ...
SAE 972841
Fuel and Additive Effects on the Rates of Growth of Combustion Chamber Deposits in a Spark Ignition Engine Gautam T. Kalghatgi Shell Research Ltd.
Copyright © 1997 Society of Automotive Engineers, Inc.
ABSTRACT Combustion chamber deposits (CCD) increase more slowly with time and take longer to stabilise in a given engine test with a base fuel compared to the same base fuel with an additive package. In a short fixed-duration test the additive might appear to increase CCD levels significantly even though the stabilised CCD levels for the two fuels are not too different. When the same additive package is used in different base fuels, the fuels are ranked in the same order with or without the additive. However, the incremental increase in CCD because of the additive is more marked the cleaner the base fuel .
additives in a manner accepted by the fuels, additives and auto industries have to be developed. Indeed, several such initiatives are in place in different parts of the world. Once such tests are developed, the relevant fuel specifications have to be agreed. This is likely to be a complex process because the effects of CCD on engine performance are not simple and not always harmful (e.g. improvements in fuel economy). This paper presents experimental results on CCD growth with different fuels and additives which have a bearing on this debate, particularly on test development. In most tests, CCD levels are determined at the end of a fixed duration test. In this work, the evolution of CCD levels with test duration is highlighted and the implications on the quantity of CCD at any given time are discussed.
1. INTRODUCTION 2 EXPERIMENTAL DETAIL Deposits, derived primarily from the fuel but with some contribution from the oil are formed inside the combustion chamber of a spark ignition engine with use. Combustion chamber deposits (CCD) cause an increase in octane requirement and, to some extent, an increase in some emissions(e.g. NOx) and a reduction in volumetric efficiency and power (1,2). However, they improve fuel economy and thus reduce CO2 emissions (2). During the past decade, the additives technology to control deposits in other parts of the engine e.g. carburetters/ port fuel injectors and inlet valves has matured and is being increasingly mandated. There has been some concern that some of this technology might cause an increase in CCD and associated engine problems. This concern became more acute during the period when a new problem, carbon rap, associated with CCD (e.g.3,4) was identified. Though this problem appears to have been largely cured by simple changes to the design of engines which suffered from it, the general interest in CCD exemplified by the 1993 CRC Workshop on Combustion Chamber Deposits (5) has not abated. There is, for instance, a desire on the part of the auto industry to bring in new fuel specifications aimed at controlling CCD levels (e.g.6). As a pre-requisite to this, tests which can be used to assess CCD formation tendencies of fuels and
The experiments discussed here were conducted in a four cylinder engine modified and instrumented for research (7,8). Deposit weight and thickness are monitored on two plugs from cylinder 1 carried in the slice between the head and the block. Figure 1 is a plan view of cylinder 1 showing the different measurement locations. The deposits were built up with the engine running at 2250 rev/min with a load of 30 Nm. Deposit Weight and Thickness: Two plugs - one near the exhaust valve (Plug 1) and the other near the inlet valve (Plug 2)- were used in these measurements. The plugs are removed at frequent intervals during a test and deposit weight and mean thickness at each of four locations, A,B,C and D (Figure 1) are determined based on at least four measurements. Of these locations, A is at the tip of the probe while B,C and D are in the squish area with the surface temperature decreasing as one moves towards the chamber wall from B to D (Figure 1). Surface temperatures are higher, and hence deposit levels
TABLE I PROPERTIES OF THE BASE FUELS USED
RON MON Density at 15 C, gm/ml RVP, mbar Aromatics, % v Olefins, %v Saturates, %v unwashed gum, mg/100ml washed gum, mg/100ml Total Sulphur, ppmw IBP, C E70, %v E100, %v E150, %v E180, %v FBP, C
FUEL F1
FUEL F2
FUEL F3
FUEL F4
FUEL F5
FUEL F6
98.6 87 0.771 752 44.1 10.6 45.3 10 1 212 32 17 36 80 95 207
98.5 87.4 0.774 701 46.3 11.6 42.1 5 1 199 30 18 36 82 96 200
100 88.5 0.791 723 57.1 4 38.9 14 1 123 31 14 28 80 96 211
98.3 87.1 0.773 739 45.6 9.2 45.2 4
