Smoke measuring apparatus

An apparatus for providing an indication of the level of smoke in an engine exhaust includes a radiation sensor which is mounted in a combustion chamber of the engine. The signal produced by the sensor during combustion of fuel is processed to produce a signal representing the period of combustion of fuel in the cylinder and this signal is applied to a map which contains recorded data showing the relationship between the combustion period and the level of smoke. From the map the level of smoke can be obtained.

This invention relates to a method and apparatus for providing an 
indication of the level of smoke in the exhaust of a compression ignition 
engine. 
A known method and apparatus for the above purpose comprises drawing a 
predetermined volume of exhaust gas through a filter paper of a given area 
and then assessing the discolouration of the filter paper. Such a test 
even with semi-automatic equipment requires time to complete so that the 
results of a particular test may not be available for several seconds. 
An alternative method involves the measurement of the opacity of the smoke 
either by sampling or looking at the entire exhaust gas flow. This is 
adequate for steady speed and load conditions where the time taken for the 
smoke to travel from the combustion chamber to the measurement zone does 
not matter but it is not suitable for use under conditions where the speed 
and load are varying particularly where the signal is intended to be used 
in an engine management system. Moreover, care has to be taken to ensure 
that the radiation responsive surfaces do not become coated with soot. 
The object of the present invention is to provide a method and apparatus 
for the purpose specified in a simple and convenient form. 
According to the invention a method of providing an indication of the level 
of smoke in the exhaust of a compression ignition engine comprises 
observing using a radiation responsive sensor, the radiation produced by 
the combustion of fuel in a combustion space of the engine, processing the 
signal produced by the sensor to provide a further signal representing the 
period of combustion of fuel in the combustion chamber and feeding said 
signal into a combustion period/smoke map for the engine to provide an 
indication of the level of smoke in the engine exhaust. 
According to a further feature of the invention an apparatus for providing 
an indication of the level of smoke in the exhaust of a compression 
ignition engine comprises a radiation responsive sensor adapted to be 
mounted on the engine so that it can observe the radiation produced by the 
combustion of fuel in a combustion chamber of the engine, means for 
processing the signal produced by the sensor to provide a second signal 
representing the period of combustion of fuel in the combustion chamber, a 
data map containing pre-recorded data showing the relationship between the 
level of smoke in the engine exhaust and the period of combustion of fuel 
and means for extracting from said data map the level of smoke which 
corresponds to said second signal.

Referring to FIG. 1 of the drawings the curves illustrate the variations 
with respect to time of the logarithm of the signal produced by a sensor 
or sensors mounted in the cylinder head of an engine, with time considered 
in terms of engine degrees of rotation, and for different fuel quantity 
levels. The sensor is of the kind described in GB No. 2193804A. If the 
time is measured from the instant of fuel delivery to the combustion 
chamber it will be seen that after the ignition delay period the amplitude 
of the radiation signal rises rapidly to a peak value from a residual 
level 7 and then decays back to the residual level as the combustion of 
fuel is completed. The decaying portion of the envelope exhibits a 
characteristic double slope and the slope of the initial portion 9 of the 
decaying portion of the envelope decreases as the amount of fuel supplied 
to the engine is increased and the time taken for the signal to decay to 
the residual level therefore increases. The slope of the initial portion 9 
of the decaying portion of the curve can be assessed but it is preferred 
to assess the so called "end of combustion point" using computer based 
techniques. The "end of combustion point" is indicated at 8 in FIG. 1 
being the point at which combustion ceases and the radiation signal 
returns to the residual level 7. 
It has been found that for a particular type of engine there is a 
correlation between the period of combustion of fuel as determined by the 
time between fuel delivery and the end of combustion point and the level 
of smoke in the engine exhaust and that it is possible to construct a map 
which shows the relationship between the period of combustion and the 
level of smoke for different engine speeds. For the purpose of 
constructing the map, the actual smoke level does have to be measured 
using one of the known techniques mentioned above. However, once the map 
has been constructed it is possible to provide a signal or reading of the 
smoke level in the engine exhaust based upon a determination of the period 
of combustion. The reading can be obtained quickly so that the process of 
smoke assessment and determination in an engine test situation is 
facilitated as compared with the known methods. As an alternative to 
assessment of the end of combustion point 8 using the aforesaid computer 
based technique it is possible to use the point at which the slope change 
takes place on the decaying portion of the envelope. 
FIG. 2 shows in block form the process of constructing the so called map. 
The engine is indicated at 10 and is supplied with fuel in timed 
relationship, by a fuel injection system indicated at 11. The engine is 
fitted with a radiation sensor 12 of the kind described in the aforesaid 
specification and the fuel injection nozzle of the combustion space with 
which the radiation sensor is associated, is fitted with a needle lift 
sensor 13 which provides an indication of the lifting of the valve member 
of the nozzle from its seating and therefore the commencement of fuel 
delivery to the combustion space. 
The signals provided by the two sensors are amplified by amplifiers 14 and 
15 respectively, the amplifier 14 being a logarithmic amplifier. The 
signals provided by the amplifiers are then subject to computer analysis, 
the first step of which is to convert the analog signals to digital 
signals in a converter 16 after which the aforesaid end of combustion 
point is determined by the use of a suitable algorithm. This process is 
illustrated as being carried out in the box 17. In order to produce the 
map 18, the engine is operated on a test basis under steady state 
conditions and a conventional smoke meter 19 is utilised to determine the 
level of smoke in the engine exhaust. The engine exhaust is sampled at 
engine operating conditions both below and above full load, and the smoke 
level reading provided by the smoke meter 19 is supplied along with the 
end of combustion point to a processing stage 20 which fixes a point on 
the map. The engine is tested at various fuel levels and speeds in order 
to produce the map 18. Experiments have indicated that the level of smoke 
is also dependant upon the instant at which fuel is delivered to the 
engine and therefore by carrying out engine tests as described but in this 
case varying the instant of fuel delivery the map produced will be able to 
provide an identification of the level of smoke for varying values of 
engine speed, the quantity of fuel supplied to the engine and the timing 
of fuel delivery. 
Once the smoke map has been produced for a particular engine it is possible 
when running or testing an engine of that type, to predict the level of 
smoke in the engine exhaust on determination of the end of combustion 
point. 
The concept of the invention can be used in vehicle engine installation in 
order to ensure that in the use of the vehicle no more than the permitted 
level of smoke occurs in the engine exhaust at conditions of engine 
operation. In a vehicle engine installation the amount of fuel supplied to 
the engine will depend upon the demand placed on the engine by the driver 
of the vehicle. However, apart from the level of smoke in the engine 
exhaust there are other limits which may not be exceeded in the use of the 
vehicle for example, the engine speed. The fuel injection system of the 
engine will therefore be controlled by a governor which will at least 
control the idling speed and the maximum speed of the engine. In the case 
of a two speed governor the amount of fuel supplied to the engine 
intermediate the idling and maximum speeds depends on the driver whereas 
if the governor is an all speed governor the driver will in effect select 
the desired engine speed and the governor will cause the fuel system to 
supply an amount of fuel to achieve or maintain that speed. In both cases, 
however, it is essential to ensure that the amount of smoke in the engine 
exhaust does not exceed the permitted level. 
In the prior fuel systems extensive engine testing is carried out to 
determine the maximum amount of fuel which can be supplied to the engine 
before the smoke level is exceeded. The fuel system can then be designed 
to ensure that no more than that maximum amount of fuel is supplied. In 
practice the actual maximum amount is slightly reduced in order to be 
absolutely sure that the smoke level will not be exceeded during the life 
of the engine and to take care of the fact that the testing may have taken 
place on a "good" engine. The aforesaid maximum amount of fuel depends on 
engine speed, air and engine temperature and the pressure of air in the 
inlet manifold of the engine testing. In addition a necessary test is a 
full load acceleration test. 
The aforesaid testing is carried out in a test cell and it is not generally 
the practice to test each production engine together with its fuel system 
following assembly. However, each fuel system is set or calibrated in 
accordance with the test results obtained. A production engine will in 
most instances, be operated at slightly less than the maximum power. If, 
however, the acutal smoke level in the engine exhaust during the operation 
of the engine can be assessed it is possible to operate the engine if so 
required by the driver, at its maximum smoke limited power. 
With the end of combustion/smoke map appropriate to the particular type of 
engine, the aforesaid mode of operation is possible. 
From the sensors 12, 13 it is possible to obtain three signals the first 
being the start of injection of fuel, the second being the start of 
combustion and the third being the end of combustion. Under cool operating 
conditions for example when the engine has just been started from cold, 
the ignition delay period is extended. The same applies even when the 
engine is hot, if a poorer quality fuel is supplied to the engine. These 
factors can be taken into account. 
In FIG. 3 there is shown a block diagram of a system for use with a 
production engine. In the diagram the same reference numerals where 
appropriate are used as are used in the diagram of FIG. 2. The fuel 
injection system 21 includes a governor which is responsive to driver 
demand as represented by an input signal 22. The system is also supplied 
with two further input signals 23, 24, the signal 23 being a timing 
adjustment signal and the signal 24 being a fuel delivery quantity 
adjustment signal. 
The signals provided by the sensors 12 and 13 are supplied to an 
analog/digital convertor 25 which includes amplifiers, the amplifier 
associated with the sensor 12 being a logarithmic amplifier. From the 
digital signals derived from the sensor signals the end of combustion 
point is determined and hence the combustion period as measured from the 
instant of fuel delivery. The computation of the combustion period is 
indicated in the diagram at 26. 
The computed combustion period together with the engine speed and the 
timing of fuel delivery are then identified on the map 18 and if the smoke 
value thus obtained is greater than the allowed value, a caculation in a 
comparison and calculation stage 27 is effected to adjust the quantity of 
fuel supplied to the engine. The timing of fuel delivery can be adjusted 
but the extent of adjustment possible is limited since, for example, 
although advancing the timing of fuel delivery will tend to reduce the the 
level of smoke in the engine exhaust, it will result in an increase in the 
level of nitrogen oxides in the exhaust. It would be more usual therefore 
to adjust the timing of delivery of fuel in accordance with engine speed 
and the fuel quantity and to use the signal 23 to effect limited timing 
adjustment. The comparison with the map 18 and the generation of the 
signals 23, 24 to adjust the timing of fuel delivery and the quantity of 
fuel delivery are effected in the stage 27. 
With the arrangement described it is therefore possible if so required by 
the driver of the vehicle to operate the engine at maximum power within 
the allowed speed range, using the smoke level in the engine exhaust as 
the controlling factor.