Method of combustion for dual fuel engine

Apparatus and a method of introducing a primary fuel, which may be a coal water slutty, and a high combustion auxiliary fuel, which may be a conventional diesel oil, into an internal combustion diesel engine comprises detecting the load conditions of the engine, determining the amount of time prior to the top dead center position of the piston to inject the main fuel into the combustion chamber, and determining the relationship of the timing of the injection of the auxiliary fuel into the combustion chamber to achieve a predetermined specific fuel consumption, a predetermined combustion efficiency, and a predetermined peak cylinder firing pressure.

BACKGROUND OF THE INVENTION 
Diesel engines efficiently convert the latent heat of hydrocarbon fuel into 
useful mechanical power. In operation of conventional diesel engines, a 
metered amount of fuel is injected into each cylinder of the engine at 
recurrent intervals synchronized with rotation of the engine crankshaft to 
coincide with the air-compression stroke of a reciprocating piston. As 
pressure increases, the compression temperature in the cylinder rises and 
the injected fuel is soon hot enough to ignite. The resulting combustion 
or firing of fuel in the cylinder forces the piston to move in the 
opposite direction, thereby applying torque to the engine crankshaft. 
Conventional engine fuel is a relatively low grade, refined petroleum known 
generally as diesel fuel oil which has desirable ignition and heat release 
characteristics. Diesel fuel oil has acceptably low levels of corrosive, 
abrasive and other noxious matter, and it is in ample supply at the 
present time. 
For nearly a century persons skilled in this art have known that coal, in 
the form of either a dry powder or a liquid slurry (i.e., a mixture of 
pulverized coal or other form of carbon dust and a liquid carrier such as 
oil or water), is an alternative fuel for diesel engines. Interest in 
developing a practical coal-fueled diesel engine has varied over the years 
directly with the cost and inversely with the supply of standard diesel 
fuel oil. For a review of such development efforts, see the article 
entitled "Slow-Speed Two-Stroke Diesel Engine Tests Using Coal-Based 
Fuels" by J. P. Davis, J. B. Dunlay, M. K. Eberle, and H. A. Steiger, 
published in 1981 as paper No. 81-DGP-12 by the American Society of 
Mechanical Engineers (New York, N.Y., U.S.A.). 
The injection of a coal-water slurry (hereinafter sometimes referred to as 
"CWS") into a compression ignition reciprocating internal combustion 
engine such as a large, medium-speed, multi cylinder diesel engine, poses 
problems not typically encountered in the injection of pure liquid fuels. 
One problem is that CWS does not ignite as readily as conventional diesel 
fuel because it has a relatively long ignition delay time, because there 
are practical limits to the degree of atomization of CWS that can be 
obtained, and because there are practical limits in the amount that the 
inlet air temperature and the compression temperature of the engine 
cylinders can be increased compared to diesel engines using standard 
diesel fuel oil as their primary fuel. 
More than 65 years ago it was recognized that a small amount of readily 
ignitable pilot fuel could be injected in diesel engines to improve 
combustion of "heavy" hydrocarbon fuels that are otherwise difficult to 
ignite. See British Patent No. 124,642. As used herein, the term "pilot 
fuel" means relatively light hydrocarbon fuel (e.g. methanol or even 
standard diesel fuel oil) characterized by being significantly easier to 
ignite than the primary fuel in the injection system. 
U.S. Pat. No. 4,825,842 disclosed a fuel injection system for an internal 
combustion engine in which diesel oil was injected as an ignition fuel and 
in which CWS was injected as a primary fuel. That patent discloses an 
apparatus which permits the use of diesel fuel either as a pilot fuel for 
CWS, or as the sole fuel for the engine. It does not, however, address the 
issue of the timing of injection of the primary CWS fuel and the ignition 
fuel, and it does not address the optimization of fuel efficiency, 
emission control and maximum cylinder pressure using those fuels. 
U.S. Pat. No. 4,612,898 discloses a cylinder head for a piston internal 
combustion engine having two fuel injection nozzles, one of which is used 
to inject an ignition fuel and the other of which is used to inject a 
main, non-self-igniting fuel. It does not, however, address the issue of 
the timing of injection of the primary CWS fuel and the ignition fuel, and 
it does not address the optimization of fuel efficiency, emission control 
and maximum cylinder pressure using those fuels. 
U.S. Pat. No. 4,700,672 discloses a two fuel injector apparatus for an 
internal combustion engine which may be used for a main fuel which is a 
liquid or gaseous fuel and a pilot fuel. It teaches that the pilot fuel 
may be injected simultaneously with the main fuel. It does not, however, 
address the issue of the timing of injection of a primary CWS fuel and an 
ignition fuel, and it does not address the optimization of fuel 
efficiency, emission control and maximum cylinder pressure using those 
fuels. 
U.S. Pat. No. 4,782,794 to Hsu et al disclosed that a small amount of 
readily ignitable pilot fuel could be injected prior to the injection of 
CWS to aid the combustion of the CWS fuel in a coal-fueled diesel engine. 
It suggested that the pilot fuel could be introduced by mixing it with the 
CWS in the fuel supply tank; or a separate pilot fuel injector could be 
used (U.S. Pat. No. 4,335,684); or the pilot and main injectors could be 
combined in one coaxial assembly (see U.S. Pat. No. 4,266,727). It also 
suggested that fuel costs would be saved (assuming that CWS fuel is less 
expensive than pilot fuel) by injecting the smallest amount of pilot fuel 
consistent with timely ignition of the CWS fuel. 
U.S. Pat. No. 4,782,794 to Hsu also discloses a fuel injection system 
particularly adapted for injecting coal slurry fuels at high pressures 
includes an accumulator-type fuel injector which utilizes high-pressure 
pilot fuel as a purging fluid to prevent hard particles in the fuel from 
impeding the opening and closing movement of a needle valve, and as a 
hydraulic medium to hold the needle valve in its closed position. A fluid 
passage in the injector delivers an appropriately small amount of the 
ignition-aiding pilot fuel to an appropriate region of a chamber in the 
injector's nozzle so that at the beginning of each injection interval the 
first stratum of fuel to be discharged consists essentially of pilot fuel 
and thereafter mostly slurry fuel is injected. 
Several articles that are of some general interest in the general subject 
matter of diesel engines or in the use of CWS fuel in combustion engines 
are listed below: 
Annand, W. J. D., "Heat Transfer in the Cylinder of Reciprocating Internal 
Combustion Engines," Proc. Instn. Mech. Engrs., Vol. 177, No. 36, 1963. 
Caton, J. A., Kihm, K. D., Seshadri, A. K. and Zicterman, G., "Micronized 
Coal Water Slurry Sprays from a Diesel Engine Positive Displacement Fuel 
Injection System," Presented to the Combustion Institute, Central States 
Section, 1991 Spring Technical Meeting, Nashville, Tenn., April, 1991 
(hereinafter "[Caton, 1991]"). 
Flynn, P. L., Hsu, B. D., and Leonard, G. L., "Coal Fueled Diesel Engine 
Progress at GE Transportation Systems," ASME Publication, Journal of 
Engineering for Gas Turbines and Power, Vol. 112, No. 3, 1990, pp. 369-375 
(hereinafter "[Flynn et al, 1990]"). 
Hsu, B. D., "Heat Release, Cycle Efficiency and Maximum Cylinder Pressure 
in Diesel Engine--The Use of an Extended Air Cycle Analysis," S. A. E. 
Transactions, 1984, p. 4.766 (herinafter "[Hsu 1984]"). 
Hsu, B. D., "Progress on the Investigation of Coal-Water Slurry Fuel in a 
Medium Speed Diesel Engine: Part 1--Ignition Studies," ASME Transactions, 
Journal of Engineering for Gas Turbines and Power, Vol. 110, No. 3, 1988, 
pp. 415-422 (hereinafter "[Hsu 1988a]"). 
Hsu, B. D., "Progress on the Investigation of Coal-Water Slurry Fuel in a 
Medium Speed Diesel Engine: Part 2--Preliminary Full Load Test," ASME 
Transactions, Journal of Engineering for Gas Turbines and Power, Vol. 110, 
No. 3, 1988, pp. 423-430 (hereinafter "[Hsu 1988b]"). 
Hsu, B. D., Leonard, G. L., and Johnson, R. N., "Progress on the 
Investigation of Coal-Water Slurry Fuel in a Medium Speed Diesel Engine: 
Part 3--Accumulator Injector Performance," ASME Transactions, Journal of 
Engineering for Gas Turbines and Power, Vol. 111, No. 3, 1989, pp. 516-520 
(herinafter "[Hsu et al 1989]"). 
Hsu, B. D. and Confer, G. L., "Progress on the Investigation of Coal-Water 
Slurry Fuel Combustion in a Medium Speed Diesel Engine: Part 4--Fuels 
Effect," ASME Publication, Coal Fueled Diesel Engines, ICE Vol. 14, 1991 
(herinafter "[Hsu 1991]"). 
Kanury, A. M., Introduction to Combustion Phenomena, Gordon and Breach 
Science Publishers, second edition, 1977 (hereinafter "[Kanury, 1975]"). 
Wahiduzzaman, S., Blumberg, P. N. and Hsu, B. D., "Simulation of 
Significant Design and Operating Characteristics of a Coal Fueled 
Locomotive Diesel Engine," ASME Publication, Coal Fueled Diesel Engines, 
ICE Vol. 14, 1991 (herinafter "[Wahiduzzaman 1991]"). 
Walsh, P. M., Zhang, M., Farmayan, W. F., Beer, J. M., "Ignition and 
Combustion of Coal-Water Slurry in a Confined Turbulent Diffusion Flame," 
presented at the 20th International Symposium on Combustion, Ann Arbor, 
Mich., Aug. 1984. 
The following methods of igniting CWS in a diesel engine were discussed in 
Hsu, B. D., "Progress on the Investigation of Coal-Water Slurry Fuel in a 
Medium Speed Diesel Engine: Part 1--Ignition Studies," ASME Transactions, 
Journal of Engineering for Gas Turbines and Power, Vol. 110, No. 3, 1988, 
pp. 415-422. (hereinafter "[Hsu 1988a]"): 
Compression ignition, in which CWS is ignited solely by the compression 
temperature generated inside the engine cylinder; 
Separate pilot diesel fuel injection, in which a separate pilot injector 
was used to supply a small amount of pure diesel fuel to ignite the CWS 
which was injected through the main injector (using two separate 
injectors); and, 
Stratified pilot fuel ignition, in which a small amount of diesel fuel is 
delivered to the cylinder through the main fuel injector where the first 
part of the fuel discharged from the injector consisted essentially of 
diesel fuel, followed by mostly CWS. Where pilot fuel was used, it was 
injected prior to the injection of the CWS fuel to aid ignition of the CWS 
fuel. 
The Hsu 1988a article described ignition studies of CWS fuel in a medium 
speed diesel engine in which the CWS fuel and pilot fuel were separately 
injected into the combustion chamber using separate injection systems. All 
of the tests were conducted under low load conditions. In the tests 
described in that article, the pilot fuel was injected either before the 
CWS fuel or at or near the beginning of the injection of the CWS fuel 
under low load conditions. 
In tests reported in [Hsu 1988a] and in [Flynn et al., 1990], preliminary 
success was obtained with a converted mechanical fuel injection equipment 
(FIE) 12 cylinder engine burning mostly coal slurry fuel. However, the 
mechanical fuel injection equipment used by that engine could provide only 
about 95% combustion efficiency, and had to use high percentage of diesel 
pilot fuel. Hsu, B. D., "Progress on the Investigation of Coal-Water 
Slurry Fuel in a Medium Speed Diesel Engine: Part 2--Preliminary Full Load 
Test," ASME Transactions, Journal of Engineering for Gas Turbines and 
Power, Vol. 110, No. 3, 1988, pp. 423-430. Flynn, P. L., Hsu, B. D., and 
Leonard, G. L., "Coal Fueled Diesel Engine Progress at GE Transportation 
Systems," ASME Publication, Journal of Engineering for Gas Turbines and 
Power, Vol. 112, No. 3, 1990, pp. 369-375 (hereinafter "[Flynn et al., 
1990]"). 
In a previous paper published by Hsu [1988a], it was pointed out that when 
pilot fuel is used to ignite CWS fuel under low or minimum load ignition 
conditions, the starting time of combustion of the CWS fuel is dictated by 
the start of pilot fuel ignition. 
As reported earlier in Hsu, B. D., Leonard, G. L., and Johnson, R. N., 
"Progress on the Investigation of Coal-Water Slurry Fuel in a Medium Speed 
Diesel Engine: Part 3--Accumulator Injector Performance," ASME 
Transactions, Journal of Engineering for Gas Turbines and Power, Vol. 111, 
No. 3, 1989, pp. 516-520 (hereinafter "[Hsu 1989]"), a high pressure 
electronically controlled accumulator injector using a diamond compact 
insert nozzle [Flynn et al., 1990] was developed. The improved reliability 
and durability of this new FIE allowed for an improved and more thorough 
study of combustion of CWS fuel in a diesel engine. It was decided to 
include a diesel pilot fuel injector in the combustion system mainly due 
to engine start and low load operation needs. As a result, the 
experimental combustion study was very much facilitated due to the ability 
of changing pilot/CWS injection timings and quantities without having to 
stop the engine. Other parameters studied included combustion chamber 
configuration (by changing CWS fuel injector nozzle hole 
number/shape/angle), as well as injection pressure. 
As the result of extensive testing, it has been determined that relatively 
small amounts of diesel fuel may be introduced into the combustion chamber 
prior to CWS fuel at minimum load conditions as a pilot fuel to ignite CWS 
fuel. Under mid-range to maximum load conditions, however, injection of 
the same amount of diesel fuel in the conventional way as a pilot fuel 
before the injection of CWS fuel does not make the CWS fuel burn in a 
timely and clean manner. Although it might be possible to introduce a 
large amount of diesel fuel to achieve timely and clean combustion of the 
CWS fuel, that would partially defeat the purpose of using the less 
expensive CWS fuel to run the engine. 
SUMMARY OF THE INVENTION 
It is an object of this invention to cleanly and efficiently burn CWS fuel 
in a diesel engine. 
It is a further object of this invention to develop a two fuel system in 
which CWS is the primary fuel and in which a relatively small amount of a 
readily combustible fuel, such as conventional diesel fuel, is used as an 
auxiliary fuel to achieve timely and complete combustion of the CWS fuel. 
It is a further objective to maximize combustion efficiency (or carbon 
burnout), while maintaining tolerable peak cylinder firing pressure 
(Pmax), and reasonable specific fuel consumption (SFC). High combustion 
efficiency is needed mainly for emissions control, although it has some 
effect also on SFC. It was previously found that due to the heat release 
concentration, or high relative cycle efficiency [Hsu, 1984] of the coal 
fuel diesel combustion, it is necessary to limit the Pmax [Hsu, 1988b]. 
Low engine SFC depends on high relative cycle efficiency and high 
combustion efficiency. However, high relative cycle efficiency usually 
brings high Pmax. Thus, it is an object of this invention to obtain a 
compromise solution to prevent engine hardware mechanical failure. 
Another object of this invention is to provide a fuel injection and control 
system that permits a turbocharged compression ignition engine to start 
and run at low power levels on diesel oil and then to transition to coal 
water slurry or other hard to ignite fuels when the turbocharger can 
supply the inlet temperature and pressure conditions necessary for 
ignition. The fuel injection system consists of two parts: (1) an 
auxiliary diesel oil system, and (2) a full load coal water slurry system. 
The engine would start, idle and run at low loads on the auxiliary diesel 
fuel system alone. When the load level necessary to achieve coal 
combustion is reached, the coal water slurry injection will be activated 
and phased in and the auxiliary diesel oil phased out as a function of 
load. 
In the preferred embodiment of the invention, two fuel systems are used in 
a diesel engine: a main fuel system and an auxiliary fuel system. The main 
fuel system uses CWS fuel. The auxiliary fuel system uses an easily 
ignitable fuel, such as conventional diesel fuel. Most of the fuel used to 
run the engine is the CWS fuel, which is less expensive than the auxiliary 
fuel. The auxiliary fuel is used as either a combustion igniter or a 
combustion enhancer, depending on the load conditions of the engine. The 
load conditions of the engine are detected by conventional detecting means 
known to those skilled in the art. 
In a preferred embodiment of the invention, a primary fuel and a high 
combustion auxiliary fuel are separately injected into the combustion 
chambers of an internal combustion engine. The timing of the injection of 
each of the two fuels depends upon the load conditions of the engine. 
Thus, the load conditions are determined first, prior to determining the 
timing of the injection of the two fuels. Under given load condition, a 
determination is made as to the amount of time prior to the top dead 
center position of the piston to inject the main fuel into the combustion 
chamber. The relationship of the timing of the injection of the auxiliary 
fuel into the combustion chamber is also determined to achieve a 
predetermined specific fuel consumption, a predetermined combustion 
efficiency, and a predetermined peak cylinder firing pressure. 
In one example of the invention, a two fuel system for a for a 
multicylinder diesel locomotive engine comprises a primary (or main) fuel, 
which is a coal water slurry, and an auxiliary fuel, which is a highly 
combustible fuel such as conventional diesel oil. The auxiliary fuel is 
used to start the locomotive engine and to run the engine at idle 
conditions or no load conditions to warm up the engines. When the engine 
is used to move the locomotive, i.e., when the engine is placed under 
load, the load conditions on the engine are detected or determined, and at 
minimum load conditions (above engine idle or above no load conditions), 
the auxiliary fuel is introduced into the combustion chambers as a pilot 
fuel prior to introducing the main fuel into the combustion chambers. At 
midrange load conditions, the amount of time required for a predetermined 
amount of evaporation and devolatilization of the main fuel under the load 
conditions is determined and the main fuel is introduced into the 
combustion chambers sufficiently prior to the top dead center position of 
the piston to achieve the predetermined amount of evaporation and 
devolatilization. The introduction of the auxiliary fuel into the 
combustion chambers is delayed relative to the introduction at minimum 
load conditions for a predetermined amount of time so that the main fuel 
can be ignited and burn very fast to yield a predetermined high combustion 
rate and efficiency. At maximum load conditions the amount of time 
required for a predetermined amount of evaporation and devolatilization of 
the main fuel is determined. The main fuel is introduced sufficiently 
prior to the top dead center position of the piston to achieve the 
predetermined amount of evaporation and devolatilization. The introduction 
of the auxiliary fuel into the combustion chambers is delayed until a 
predetermined amount of time after introduction of the main fuel has 
occurred so that the main fuel has evaporated and so that the main fuel 
will burn very fast to yield a predetermined high combustion rate and 
efficiency at a predetermined maximum cylinder pressure. Thus, in some 
cases, at maximum load conditions, the main fuel will self ignite prior to 
the introduction of the auxiliary fuel and the auxiliary fuel will act as 
a combustion enhancer, rather than as a pilot fuel. 
The coal water slurry may comprise from about 0.7% to about 2.5% ash and 
the solid loading of the slurry may comprises from about 47% to about 49% 
by weight. 
Also, in a preferred embodiment of the invention, a separate, independent 
auxiliary fuel injection system is provided to start and run the engine at 
low load on a readily combustible fuel, such as conventional diesel oil, 
and another independent primary fuel injection system is provided to 
inject less combustible fuel, such as CWS, once the engine reaches normal 
operating conditions. Throttle means are provided to select the load under 
which the engine operates. Sensing means, such as a transducer, are 
disposed in operative communication with the cylinder, either directly or 
through other parts of the engine, to determine the operating condition of 
the engine. Control means responsive to the sensing means and throttle 
means, such as an electronic circuit or other commonly known computer 
controls are in communication with the auxiliary fuel injection system and 
the primary fuel injection system and selects the amount of CWS fuel and 
diesel fuel to be injected into the engine cylinders and the timing of 
their respective deliveries in accordance with the method described above.

DETAILED DESCRIPTION 
FIG. 1 is a diagram depicting the components of a typical combustion 
chamber of a multicylinder diesel engine that are relevant to this 
invention. Cylinder 10 of the combustion engine houses a reciprocating 
piston 12 which is operatively connected to a crankshaft (not shown) as is 
well known those skilled in the art. The combustion chamber 14 of the 
cylinder 10 consists of the area in the cylinder between the top 16 of the 
piston 12 and below the cylinder head 18. 
Cylinder 10 is provided with means for introducing the main fuel into the 
cylinder, which may comprise a main fuel injector 20, which may be made in 
accordance with the invention previously disclosed in U.S. Pat. No. 
4,782,794 to Hsu. That fuel injection system was particularly adapted for 
injecting coal slurry fuels at high pressures and includes an 
accumulator-type fuel injector which utilizes high-pressure pilot fuel as 
a purging fluid to prevent hard particles in the fuel from impeding the 
opening and closing movement of a needle valve, and as a hydraulic medium 
to hold the needle valve in its closed position. 
Cylinder 10 is also provided with a separate means for introducing the 
auxiliary fuel into the cylinder, independent of the main fuel, which may 
consist of an auxiliary fuel injector 22, such as any conventional diesel 
fuel injectors which are well known to those in the art. 
Cylinder 10 may also be provided with detecting means, such as a 
transducer, for detecting the pressure and/or temperature conditions of 
the cylinder. 
As is known to those in the art, conventional diesel engines typically have 
a crankshaft mechanically coupled to a variable load such as the rotor of 
an alternating current generator that supplies electric power to an 
electric load circuit. The power output of the generator and hence the 
load imposed on the engine crankshaft is limited by a regulator. The 
engine typically has multiple sets of two cylinders in which reciprocating 
pistons are respectively disposed, the pistons being respectively 
connected via rods and journals to individual eccentrics or cranks of the 
crankshaft. In a typical medium speed 4,000-horsepower engine, there are 
16 cylinders, the cylinder bore is approximately nine inches, and the 
compression ratio is of the order of 12. Each cylinder has air inlet and 
exhaust valves (not shown) that are controlled by associated cams on the 
engine camshaft which is mechanically driven by the crankshaft In a 
4-stroke engine, the camshaft turns once per two full revolutions of the 
crankshaft, and therefore 2:1 speed reducing gearing is provided. 
As was disclosed in U.S. Pat. No. 4,782,794 to Hsu, the amount of CWM fuel 
discharged into each cylinder during each injection interval varies with 
the angular position of a fuel control shaft connected via a parallel 
array of cranks to adjusting rods of a family of fuel pumps that are 
individually associated with the respective injectors. The fuel control 
shaft is coupled by a linkage to suitable actuating means for turning it 
to the desired position, as indicated by the value "X" of a variable 
electrical input signal supplied to the actuator by control means. 
In one embodiment of this invention, a multi-cylinder diesel engine has 
cylinders having a 229 mm bore, a 267 mm stroke and a rated speed of 1050 
rpm. The combustion chamber 14 has a side mounted pilot diesel fuel 
injector 20 and a centrally placed CWS main fuel injector 22. The pilot 
fuel injection system and the main CWS fuel injection systems are 
conventional systems known to those skilled in diesel engine systems and 
are controlled by conventional electronic control systems, also known to 
those skilled in diesel engine systems. The injection timings and 
quantities can be varied by those systems in accordance with the invention 
described below. 
One example of CWS fuel which may be used in practicing this invention was 
coal cleaned to 0.8% ash as shown in Table 1. The solid loading of the 
slurry used was maintained at about 49% by weight. It is also possible to 
use CWS fuel having a range of 0.7% ash to 2.5% ash. The slurry may be 
varied from about 46% to about 51% by weight, but preferably is in the 
range of about 47% to 49% by weight. 
TABLE 1 
______________________________________ 
Analysis of Coal Used in Coal Water Slurry 
______________________________________ 
Proximate Analysis Ultimate Analysis 
% Ash 0.80 % Carbon 82.59 
% Volatile 39.40 % Hydrogen 5.34 
% Fixed Carbon 
59.80 % Nitrogen 2.08 
Particle Size % Chlorine 0.18 
Mass Mean Diameter 
5.47 % Sulfur 1.01 
(microns) % Oxygen (diff.) 
8.00 
Heating Value High Heating Value 
34630 
(kJ/kg) 
______________________________________ 
FIG. 2 shows the combustion analysis of three runs under engine full load 
conditions (high inlet air temperature and pressure) using the same CWS 
fuel injection timing of 25 deg BTDC while varying the pilot fuel timing 
from 35, 25 to 15 deg before top dead center (BTDC). As already proven by 
previous work, the first small peak on the heat release trace corresponds 
to the combustion of the pilot fuel. The start of the rise of the heat 
release trace that follows immediately afterwards indicates the start of 
combustion, or ignition, of the CWS fuel. It is clearly seen that the 
overall start of combustion in the engine depended on the pilot fuel 
timing. It is also seen that, although the CWS fuel was injected at the 
same timing, the CWS fuel residence time before coal ignition (from the 
start of CWS injection to coal ignition time characterized by the start of 
the second rise of the heat release curve) depended on the pilot fuel 
timing. 
In the right side upper table in FIG. 2, the test conditions are listed. In 
the lower table of "Combustion Results", the criteria set forth to 
investigate combustion in this study (Pmax, combustion efficiency, and 
SFC) are listed. The run with 15 deg pilot injection timing had the most 
favorable combustion. It had the lowest Pmax, highest combustion 
efficiency, and lowest SFC. Some of the results can find explanation from 
the heat release traces. The highest Pmax (35 deg BTDC pilot timing case) 
was caused by the large amount of fuel burning BTDC. Fuel burned BTDC has 
a predominant effect on Pmax than that burned after TDC (ATDC) [Hsu, 
1984]. The lowest SFC (15 deg BTDC pilot timing case) can be explained by 
the concentrated fuel combustion close to TDC, as indicated by the highest 
"Relative Cycle Efficiency" of 92.4% listed in the same table. The effect 
of the latter has also been explained by Hsu [1984]. In FIG. 3, the 
cylinder pressure and temperature are plotted together with the heat 
release rate. The case of 15 deg BTDC pilot timing produced the highest 
maximum temperature occurring at about the end of the heat release period 
(30 -40 deg ATDC), which probably contributed to the highest combustion 
efficiency obtained. 
The difference in the shape of the three heat release traces is believed to 
be caused by the variance of CW fuel residence time before coal ignition, 
which is shown in Table 2. The residence time of CWS before ignition 
appears somewhat like the "ignition delay" for diesel fuel. However, the 
processes involved are very different. With normal diesel fuel operation, 
during the ignition delay period, both a physical evaporation process and 
a chemical kinetic reaction process take place (mainly the latter which 
depends on the fuel cetane number). For CWS fuel, the residence time is 
mainly needed for water evaporation. This is observed both in an engine 
study [Hsu, 1988a] and a furnace study [Walch et al., 1984]. The amount of 
dehydrated coal fuel that can be burned at ignition time depends on the 
amount of water evaporated at that instant. Clearly, the longer residence 
time the CWS fuel has in the cylinder before ignition, the more water is 
evaporated by the heat in the cylinder. Thus, more dehydrated coal is 
released for combustion immediately after ignition. Hence, a very high 
concentrated heat release rate could appear. On the other hand, it should 
be pointed out that when pilot fuel is injected early and starts to burn, 
the average cylinder temperature becomes higher at an earlier time, which 
can also accelerate evaporation. This can be seen for the three cases in 
FIG. 3 and the average gas temperatures in the cylinder during coal 
residence time before ignition are listed in Table 2 as well (both in 
crank angle degree and absolute time scales). However, the higher 
temperature has less effect on evaporation than the residence time. This 
can be explained, on one hand, by the simplified basic droplet evaporation 
relationship as follows [Kanury, 1975]: 
EQU dW=k1*ln(k2*Tcyl+C) 
dW--increment of evaporated water mass 
dt--time increment 
Tcyl--in cylinder temperature 
k1--f(droplet diameter, thermal diffusivity, density) 
k2--f(specific heat, latent heat) 
C--f(specific heat, latent heat, droplet temperature) 
In the above formula, it is seen that the in-cylinder temperature affects 
the evaporation mass in the exponential term, whereas, the residence time 
has a direct proportional effect. On the other hand, Table 2 indicates 
that the difference in average gas temperature for the three cases is very 
small (from 940 to 920K, about 2%). However, the order of magnitude of 
change in the residence time available for evaporation is significantly 
greater (from 0.95 to 2.38 msec, about 250%). Thus, due to having the most 
amount of available dehydrated coal fuel at ignition, the case of 15 deg 
pilot injection producing the highest and most concentrated heat release 
rate is understood. 
TABLE 2 
______________________________________ 
Residence Time and Average Temperature Before Ignition 
CWS Fuel 
Pilot Fuel Res Time Avg Cyl 
Timing Deg CA Gas Temp 
Deg BTDC (msec) Deg K 
______________________________________ 
35 6 (0.95) 940 
25 11 (1.74) 930 
15 15 (2.38) 920 
______________________________________ 
From the above analysis, it is seen that CWS fuel can be ignited by pilot 
fuel anytime after being injected into the engine cylinder. However, the 
best combustion result was obtained by delaying the ignition as much as 
possible, as in the 15 deg pilot injection case. This can be appropriately 
named the "Delayed Ignition" case. In fact, the computer combustion model 
study under our general research contract also suggested the CWS fuel be 
injected highly in advance of the pilot fuel [Wahiduzzaman et al., 1991]. 
In the engine tests, it was also found that when pilot injection was 
further retarded, self ignition of CWS occurred, which was the limit of 
"Delayed Ignition". In such instances, pilot fuel no longer ignited the 
coal fuel, but rather enhanced combustion after coal self ignition. No 
detrimental effect on combustion or engine performance was observed for 
these cases either. 
Since CWS self ignition is the limit of "Delayed Ignition", a further study 
was conducted to investigate ways to increase the self ignition delay of 
CWS fuel. One obvious way is to advance the injection timing of CWS fuel. 
Test runs were made by retarding the pilot injection timing beyond the 
self ignition of CWS fuel. The results of these tests are shown in FIG. 4. 
Clearly, ignition delay increases as CWS injection timing is advanced 
(lowest curve). This is evidently due to lower mean in-cylinder 
compression temperature which the CWS experiences during the delay period. 
The mean in-cylinder temperature for the cases studied is shown on the 
upper curve. Interestingly, the actual ignition time in terms of crank 
angle position did not change much as shown by the middle curve. 
However, test results showed overly advanced injection timing, although 
providing very long delay, also deteriorated combustion and engine 
performance. The combustion analysis of the test cases are shown in FIG. 
5. From the combustion results table in the lower right side of this 
figure, comparing the 1st (22 deg CWS inj., run #31) and the 2nd (32 deg 
CWS inj., run #33) case, SFC is clearly in favor of run #33 which had the 
longer delayed ignition. The combustion efficiency of the two are the 
same, while the Pmax of run #31 is much lower. This is because of the much 
lower heat release rate (solid line) due to short "Delayed Ignition". This 
trend did not hold true for further advancing the CWS injection timing 
from 32 deg BTDC to 42 deg, as shown by the third case (run #39, center 
line). For this last run, although Pmax remained the same, the combustion 
efficiency and SFC started to deteriorate (from 99.5% to 99.1% and from 
8054 to 8876 kJ/kWh respectively). Further advancement of CWS injection 
timing to 47 deg BTDC (not shown in the figure) had drastically caused the 
combustion efficiency to drop to 98% and SFC to increase to over 9100 
kJ/kWh. 
The reason for the combustion deterioration cannot find explanation in the 
normal pure diesel fuel operation experience. Overly advanced injection 
timing in diesel fuel operation brings BTDC early combustion, which leads 
to high Pmax, diesel knock (long ignition delay), and bad SFC. In the coal 
fuel engine case, no overly early combustion is detected. By reviewing the 
data of a separate CWS fuel injection study included in the present 
contract [Caton, 1991], it is highly probable that the CWS fuel spray has 
reached the cold cylinder liner walls by the time of ignition for the very 
early injection timing case. This is illustratively shown in FIG. 6. 
Further analysis had shown that, even with the 32 deg injection case, CWS 
fuel spray should have hit the piston crown after less than 5 degree crank 
angle. The CWS was not ignited until at least 20 crank angle degrees later 
(about 10 deg BTDC). Therefore, piston crown impingement happened well 
before ignition. Probably the crown temperature was high enough not to 
deteriorate the overall vaporization and subsequent combustion. Inspection 
of piston crown after engine dismantling had shown definite impingement 
marks. A major difference in the combustion of CWS and pure diesel fuel in 
the engine may be that for the CWS case, fuel spray impingement is not 
only unavoidable, but, in fact is necessary (for "Delayed Ignition"). 
Fuel injection timing maps for full engine load operations have been 
generated for Pmax, combustion efficiency, and SFC, as shown in FIG. 7. 
They are made by generating isometric lines using actual test results 
(triangles in the figure). For all the three indicators, in the full load 
usable range, pilot fuel injection timing seems not to have a major 
effect. This is probably due to the fact that, the combustion in the 
engine cylinder is mostly initiated by coal fuel self ignition. At about 
37 deg BTDC CWS injection timing, maximum Pmax can be expected with each 
pilot fuel injection timing. The later the pilot fuel is introduced, the 
smaller its contribution to raising Pmax due to ATDC combustion. 
Introducing the CWS fuel before 37 deg BTDC (towards the right in the 
map), Pmax is reduced because of fuel spray cylinder liner impingement 
hindering heat release rate. CWS fuel "Delayed Ignition" effect again can 
be seen in the part where injection is after 37 deg BTDC (towards the 
left). The same explanation can be given to the combustion efficiency and 
SFC part of the map. However, the optimum CWS injection timing for these 
two indicators are not the same. This is probably because the optimum 
combustion efficiency depends mainly on the cylinder temperature, whereas 
the SFC depends on the concentration of heat release about TDC ("Relative 
Cycle Efficiency") and the combustion efficiency. Using this map, the 
injection timings of pilot and CWS fuel can be selected with the 
compromise needed for Pmax, combustion efficiency, and SFC. In the present 
case, the pilot timing is 12 and the CWS timing is 35 deg BTDC. 
The first investigation on combustion chamber configuration was to compare 
a 10 hole (0.40 mm dia.) CWS injector nozzle with an 8 hole (0.46 mm dia.) 
having the same total flow area. The combustion indicators are summarized 
in FIG. 8. It is seen that, both the injectors can have the same maximum 
Pmax value, same highest combustion efficiency, and lowest SFC. Only, they 
happened at different CWS injection timings. Normal pure diesel fuel 
operation experience would suggest the better "air utilization" of the 10 
hole injector nozzle should indicate some advantage. Further investigation 
into the fuel injection rate of the nozzles had shown that due to the hole 
size discrepancy, the hole discharge coefficients were different (0.88 for 
the 0.40 mm hole and 0.80 for the 0.46 mm hole). Since they were injected 
with the same injection pressure of 82.7 MPa, the spray exit velocity from 
injector hole for the former was 333 m/s, and the latter, 300 m/s. The 
higher exit velocity 10 hole nozzle would hit the cylinder liner wall at a 
smaller injection advance angle making its optimum value move 
correspondingly. This explanation suggests that for the two injectors 
tested, the initial air entrainment of the spray jet (hole number 
dependent) is not as important as the secondary atomization after spray 
impingement (depending on spray velocity) on the piston crown. Similar 
tests were done with different injector hole shapes. They included inverse 
trumpeted hole, rounded inner edged hole etc. Both 8 and 10 hole nozzles 
of different shapes were made. All of them seemed to suggest the same 
conclusion of spray velocity having the dominant effect. Based on these 
results, the 8 hole nozzle was selected for prototype due to much less 
tendency to hole plugging. 
An 8 hole nozzle with smaller spray included angle of 130 degrees (as 
compared to the original 150 degrees) was tested to avoid cylinder liner 
impingement of CWS spray. It is schematically shown in FIG. 9. Test 
results as compared with the original are shown in FIG. 10. It can be seen 
that the firing pressure was lower and the combustion efficiency never 
reached the previous level, although the SFC was close. However the fact 
that the combustion efficiency decreased was not acceptable to the 
combustion design. This may imply that too much attachment of the impinged 
CWS on the piston crown is unfavorable also. More work has to be conducted 
in the future to optimize CWS impingement in the combustion chamber. 
An investigation into CWS injection pressure was conducted early in the 
combustion study. The injection pressure varied between 61 to 83 MPa. The 
Pmax, combustion efficiency, and SFC results are compared in FIG. 11. Pmax 
and combustion efficiency are seen to increase with CWS injection 
pressure, while SFC decreases. Within the tested range, combustion 
performance definitely improved when higher injection pressure was used. 
The calculated heat release traces together with the cylinder pressure and 
the injector needle lift of the three runs are shown in FIG. 12. The 
highest heat release rate of the highest injection pressure case is 
evident. The injection starting times was the same (25 deg BTDC) and the 
CWS fuel was ignited at about the same time (10 deg BTDC). The higher heat 
release rate after ignition started is both the result of better 
atomization and more fuel being injected into the cylinder at the same 
instant. It is interesting to note that from the CWS ignition to the fall 
off of the peak heat release, there seems to be a fairly constant duration 
of 35 to 40 degrees crank angle. If the injection duration extends beyond 
the fall off period, then a hump, mentioned first by Hsu [1989], of rather 
slow heat release rate appears towards the end of the combustion period. 
It is in proportion to the extension of fuel injection duration beyond the 
35 to 40 degrees crank angle period. 
Lower load operation is characterized by very low or no boost pressure in 
the inlet air manifold. As explained previously [Hsu, 1988a], it is not 
possible to self ignite the CWS due to the excessive temperature drop 
after heat is extracted to vaporize the water in fuel. Pilot diesel fuel 
combustion heat is necessary to raise the temperature early in the cycle 
for water evaporation. A typical combustion heat release pattern of the 
notch 2 load (naturally aspirated, 536 rpm, 300 kPa BMEP) is shown in FIG. 
13. The first triangular heat release shape corresponds to the pilot 
diesel fuel combustion, which amounts to about 24% of energy as compared 
to about 4% at full engine load. The coal combustion efficiency was only 
about 93%, due to the low maximum combustion temperature of 1560K which is 
much lower than the 1900K at full engine load. The engine operation 
conditions and performance results at lower loads are summarized in Table 
3. 
TABLE 3 
__________________________________________________________________________ 
Engine Operation Conditions and Results 
Operation Conditions Combustion Results 
MEP Inj. Tim. BTDC 
Fuel Amt Percent 
Pmax 
Comb. 
SFC 
Load 
RPM MPa Pilot 
CWS Pilot 
CWS MPa Eff. % 
kJ/kWh 
__________________________________________________________________________ 
N2 620 0.30 
24 15 23.8 
76.2 4.9 92.8 
12165 
N3 880 0.49 
23 15 23.9 
76.1 5.5 94.9 
10450 
N4 880 0.56 
22 15 16.9 
83.1 5.9 96.5 
9255 
N5 960 1.03 
20 20 9.2 90.8 8.2 97.5 
8560 
N6 960 1.35 
19 20 6.7 93.3 9.9 98.5 
8258 
N7 960 1.71 
18 25 5.0 95,0 12.3 
99.0 
8403 
N8 1050 
1.98 
12 35 4.0 96.0 17.1 
99.5 
8159 
__________________________________________________________________________ 
It is most interesting to note that when engine load increases, the optimum 
injection timing of the pilot fuel is retarded while that of CWS fuel is 
advanced. As anticipated, the pilot fuel amount needed becomes less when 
engine load is increased. The combustion efficiency increases with the 
engine load probably due to higher combustion and piston crown 
temperature. 
Within the present program, a duty cycle coal usage percent target had been 
set for the study of overall economics of a coal fired locomotive. A 
typical locomotive operates about 60% of time at idle, which uses pure 
diesel fuel. Therefore, the target was set for 75% of coal energy 
consumption (25% diesel fuel) on a duty cycle basis. The above Table 3 
type of operation can actually provide 80% coal usage, which exceeded the 
planned goal. 
Apparatus for practicing this invention is shown in block diagram form in 
FIG. 14. An internal combustion engine, which may be a diesel engine, as 
depicted in FIG. 1. The cylinder has a combustion chamber defined by the 
space between the top of the piston head, the cylinder walls and the 
cylinder head. The cylinder is provided with two fuel injectors; one for 
the main fuel and the other for the auxiliary fuel. Each of those fuel 
injectors is operatively connected to fuel injection systems. Fuel 
injection systems for the auxiliary fuel, which may be diesel fuel, are 
well known in the art. Fuel injection systems for the CWS fuel are shown 
diagrammatically in FIGS. 15 and 18. 
Sensor means, which may be pressure transducers, temperature sensors, 
and/or engine crank angle encoders are provided in communication with the 
combustion chambers, and/or the crank, and/or the linkage of the engine, 
and/or the throttle. Control means, which may be a computer or any 
microprocessor driven device, are in communication with such sensor or 
sensors. The control means are operatively in communication with the fuel 
injection systems, and control those systems in response to the throttle 
input. The general layout of the engines is shown in FIGS. 16, 17 and 19.