| Preface
In Part-X of this 'series', I'd shared with you some thoughts and real
life experience about different kinds of problems one can run into while
maintaining one's Car.
Well, there're some more ..
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1)
Some Diesel/Petrol Engine fundamentals
Diesel
engines, as the name implies, run on diesel oil as their fuel and Mpfi's
- an upgrade of the conventional carburettor types - are petrol driven
ones. The eqvt of Mpfi in diesels is 'Crdi' - or the 'Common rail direct
injection'.
Diesel engines - whether conventional or Crdi - run on the principle of
'compression ignition' and have no need for an electrical spark ignition
system deploying an Ignition Coil and a Distributor plus Spark Plugs etc.
For some time now, ‘distributor-less’ ignition systems are
in vogue – such as in MUL Wagon-R, Baleno and the likes in other
makes.
Diesel engines suck in plain/filtered air and compress it to a high degree
- of the order of 22:1 - which results in the air so compressed inside
the cylinders attaining very high temperatures at the end of their 'compression
stroke', when a pre-meditated quantity of diesel oil is 'squirted' into
the cylinders by fuel 'injectors' and it ignites instantaneously.
On the other hand, Petrol engines due to lower flash point of Gasoline
normally have compression ratios of the order of 8-10:1 and compress an
air/fuel ‘mixture’ that's drawn in and closer to the end of
the compression stroke, it's ignited by an electrical spark generated
by a dedicated Ignition System.
Further, given the different 'flash-point' of the two, 'stock' petrol
engines today have a/limiting compression ration of 9-10:1 and naturally
aspirated diesels ~ 22:1. Turbo diesels, depending on their design, can
have lower, down to ~ 16-17:1.
For more insights into the working of Mpfi's (and in principle of Crdi's),
you're welcome to surf our following URL -
http://www.indiacar.com/infobank/mpfisystems.htm
2)
How does an Engine Start
For simplicity’s sake, it's just like a Bike which ‘starts’
when you kick it - with its ignition AND fuel switched on !
Coming to a Car with a 'multi-cylinder' 4-Stroke engine, not that a 2-stroke
would make any difference, let's look at the following fundamentals :
1) We all know that an ICE has a piston inside its cylinders 'connected'
to the 'Crank-shaft' by means of connecting rods. This way, the reciprocating
motion of the pistons is converted into a rotary one of the Crankshaft
- just like the exposed ones of a Railway Steam Loco.
2) The top-end of a piston's stroke is known a 'top-dead-centre/TDC' and
like wise the bottom/BDC.
3) A 4-S/ICE has to have a minimum of 1-Inlet Valve and 1-Exhaust Valve.
These valves are opened/closed at the designed 'timing' by the 'Camshaft',
which is driven by the Crankshaft at 1/2 its rpm by means of either a
'timing-chain' or a 'toothed rubber belt' - as in most Cars today.
4) Stroke 'one' of a 4-S/ICE is called the 'suction stroke'. This happens
when the piston moves downwards from its TDC with the inlet valve open.
This allows it to 'suck-in' appropriate mixture of Air and Fuel - either
via a Carburettor OR by 'injection' as in Mpfi Cars today. When the piston
reaches the BDC, the inlet valve closes.
5) On its rtn stroke from such a BDC, the piston begins to 'compress'
the A/F mixture it drew-in in the previous stroke AND during this stroke,
both its I/E valves are closed. This/'Stroke-2' is called the 'Compression
stroke'.
6) Just before it reaches the TDC - a point calculated by design/experience
- the Electrical Ignition System of the Car sends a high voltage pulse
to its Spark Plug. The pulse is strong enough to enable it 'jump across'
the SP's calculated/pre-set 'gap' inside the Cyl.
7) Such a spark ignites the explosive A/F mixture within the Cylinder
which is already compressed 12 to 13 times the Atmospheric pressure by
now and it goes off like a bomb inside the cylinder. Both the I/E valves
are still closed.
8) Since such explosive gases are so 'contained' within the cylinder,
the piston gets pushed back to its BDC with all their force after it reaches
its TDC on the upward stroke. This/'Stroke-3' is called the 'Power Stroke'.
9) Just when the Piston so hits its BDC, only the Exhaust valve is opened
via the Camshaft and on it's such upward stroke #4 - the 'Exhaust stroke'
- the burnt/expended gases are 'driven out' of the cylinder via the tail
pipe by the time the piston reaches its TDC. At this point, the Camshaft
closes the exhaust valve and soon thereafter - opens the Inlet Valve for
the suction stroke to commence as per (4) above and the entire ‘cycle’
repeats itself.
Hereafter, having been so 'cranked' either by a pedal kick or an Electrical
Starter Motor - provided it's revved to atleast half its designed idling
speed and A/F mixture+Electrical Spark is available as per its needs -
the engine can continue to run by itself. In other words, it has 'started'.
3)
The ECU and ‘# of Bits’
The choice of # of bits depends largely on the individual OEM design philosophy
and it's inter-debatable as to which System is superior. For example,
for EU-II cars,’ Hyundai followed 8-bit designs and MUL used to
tom-tom that their 16-bit design is superior to Hyundai's - but no longer
so when FIAT turned up with its 32-Bit ECU's – all for EU-II’s.
On the otherhand, to meet the more stringent emission requirements of
EU-III, faster responses for ‘engine management’ were called
for from such ECU’s and today, almost all EU-III’s have 32-bit
‘EPROMs’. There are some informative Articles on Mpfi Systems
for Cars posted under 'Infobank'. I'd suggest you Surf these for additional
insights into this subject.
As for 'Self-diagnostics' of any Mpfi Engine mal-function, these practices
vary from OEM to OEM. Some have provision for displaying 'Error-Codes',
after a certain 'procedure', in the designated window on the Car's Dashboard
and some require a custom-built Palm-Top type ‘ECU Analyser’,
available with their Dealerships. Such units, when plugged into the 'Test
Socket' provided for the purpose under the Dashboard of a Car, can pin
point a fault in the engine management system to enable a corrective action.
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