Design Features and Effects of Ignition Timing on Internal Combustion Engine

This article discusses the design features of an internal combustion engine, including the use of a double overhead camshaft, variable valve timing intelligence, and multipoint fuel injection. It also explores the effects of advancing or retarding the ignition timing, coolant type, and octane rating of fuel on the engine's performance. The article provides insights into the advantages and disadvantages of the engine's design and the optimal operating temperatures.

Running Head: Internal combustion engine
Running head: Internal Combustion Engine
Name
Course
College

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Ford Falcon ‘Barra’ Inline 6-cylinder petrol engine with dual cam VVT, multipoint
sequential fuel injection and coil on plug electronic ignition. The engine is also fitted with 2
‘knock’ sensors
 Bore: 92.26 mm
 Stroke: 99.31 mm
 Displacement: 3984 cc
 Number of valves: 24
a) Discuss in detail the general design features of the engine (according to these
apparatus). Why choose this apparatus to design and its advantages and
disadvantages. It is the under square type ( Stroke
Bore
), so why design use this type.
Solution
The engine is served by a double overhead camshaft (DOHC) for efficient opening and
closing of the engine valves. This design eliminates the need for a pushrod which normally
tend to create flexes; it also reduce mass in the valve train ensuring that the engine runs safer
and cleaner.
Each cylinder is served with four valves (in a ratio of 2:2 for the inlet and outlet) thus
ensuring efficient intake and exit of the combustion products. The double camshaft have a
direct contact to the valves hence accurate opening of the valves. This is also facilitated by
the variable valve timing intelligence (VVTi).
The stroke ratio of the engine is 0.93 hence it is an under square (long stroke) type. This
cylinder design ensures high engine efficiency and higher fuel economy. The high volume to
surface area ratio reduces heat loss from the combustion chamber and increases brake-
specific fuel consumption (BSFC) (Alkidasa & J, 2003). It also exhibit the highest torque at

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lower revolutions of the crankshaft (rpm) because of their longer crank throws and high
piston speeds, thus they have gained familiarity to most manufacturers.
The multipoint fuel injection ensures efficient fuel distribution to all the cylinders, thus
ensuring cleaner combustion due to accurate fuel metering. The coil-on-plug ignition ensures
maximum utilization of the waste sparks. This coil mounted on a spark serves two cylinders
thus ensuring that both cylinders are served regardless of their relative position.
The two knock sensors, which are usually threaded to the engine block, cylinder head or
the intake manifold, help detect any notable engine knocks that may result into engine failure
thus through signal transmission to the power train control module (PCM) the ignition timing
is altered (advancing or retarding it).
b) Why has this engine been equipped with two camshafts?
Solution
The double overhead camshaft regulate the opening and closing of the valves: one for the
inlet valves and the other for outlet valves, thus ensuring timed control of all the 24 valves.
This system is also connected to a VVTi, an electronic system that ensures just a timed and
accurate firing in the combustion chamber.

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Part B: Analysing Effects of variations in ignition timing.
Engine speed(N-
RMP)
Average torque
(Nm)
crankshaft angle
850 90 
10-
1000 120 
0
1200 180 
10
1250 230 
35-
According this form to answer questions
Solution
1. Discuss the effects of advancing or retarding the ignition timing.
Retarding the ignition timing by -100 at a relatively lower speed results into the lowest
torque output as compared to advancing it by the same degree. This is because the spark
is created at a condition when the piston has expanded thus leading to lower torque
caused by power loss. Retarding the timing by -350 ensures the highest output torque of
about 230 N.m at a speed of 1250 rpm. This shows that the retardation angle was the right
angle to ensure maximum power output. Therefore, ensuring improved engine longevity,
fuel economy, and maximized engine power (Willard, 1998).
2. Discuss the effects of coolant type and indicate your understanding of optimal
operating temperatures.

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Maximum engine performance (maximum torque at maximum speed) is realised
when the best coolant is used within the cooling passages to take away heat generated
by the combustion process. Poor coolants, which tend to freeze in cold weather,
without a uniform and free flow and also those of poor composition; this causes
inefficient cooling hence making them run very hot, misfiring of the sparks or a boil-
over. Good coolants will ensure the engine operates at optimal operating
temperatures, thus minimizing cases like boiling of coolant, overheating and eventual
component failure.
3. What is the optimum ignition timing for an engine and by what parameters is it
limited? Ans: for example engine speed, engine fuel, knock, etc.
The best ignition timing occurs at maximum torque of 230N.m hence a crankshaft
angle -350. At this point maximum torque is realised at maximum speed hence any
further increase in engine speed may lead to a knock thus causing engine failure
(Alkidasa & J, 2003). Very high speeds of the crankshaft requires larger timing
timings while on the other hand very low speeds makes the timing inefficient.
4. How does the octane rating of the fuel affect torque output and why?
Fuels with higher octane numbers have a characteristic lower torques as shown in the
form. This is because such fuels tend to burn at very high temperatures than those
with lower ratings.

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References
Alkidasa, C., & J, P. M. (2003). Transient Heat-flux measurements in the combustion
chamber of a spark ignition engine. Journal of Heat Transfer, ASME Trans., 62--67.
Willard, W. P. (1998). Engineering Fundamentals of the Internal Combustion Engine (3rd
ed.). New Jersey : Prentice Hall Publishers.