An engine using octane air mixture has N2, O2, CO2, CO and H2O as constituents in the exhaust gas. Which one of the following can be conceded?
Increase of O2 and CO in flue gas analysis indicated incomplete combustion.
Knocking in spark ignition engine can be reduced by
When the spark is advanced, burning gas is compressed by the rising piston and therefore temperature and pressure are increased, thus tendency to knock increases. But by retarding the spark timings the peak pressure are reached further down on the power stroke and thus tendency of knock in SI engine decreases.
The ignition of the charge by some hot surface within the engine before the passage of spark is called
The surface ignition occurs before the passage of the spark is called pre-ignition. Pre-ignition generally caused by an overheated spot which may occurs at the spark plug, combustion chamber deposits or exhaust valves. Mostly spark plug is very prone for pre-ignition because very high temperatures in the order of 1100°C are required to produce pre-ignition.
For minimizing knocking tendency is SI engine, where should be spark plug be located?
For minimizing knocking tendency in SI engine spark plug should be located near the exhaust valve.
The delay period in Cl engine depends upon which of the following?
Delay period is affected by the following factors:
(ii) Injection pressure or size of droplet
(iii) Injection advance angle
(iv) Compression ratio
(v) Intake temperature
(vi) Jacket water temperature
(vii) Fuel temperature
(viii) Intake pressure or super charging
(x) Air-fuel ratio
(xi) Engine size
(xii) Type of combustion chamber
The tendency of knocking in LC. engine reduced by
Injection of fuel just before TDC will have high temperature surrounding so less delay period.
Increasing the compression ratio in Si engines the knocking tendency
Increasing the compression ratio increases both the temperature and pressure. Increase in temperature reduces the delay period of the end gas hence tendency to knock increase.
Decreasing the cooling water temperature in SI engines, the knocking tendency
Detonation in SI engines occur due to
Desirable characteristics of the combustion chamber for SI engines to avoid knock is
In Cl engines with increase in compression ratio the delay period
Increase in compression ratio, reduces the delay period as it raises both temperature and density.
Knocking takes place in Cl engines
In Cl engine detonation occurs near the beginning of combustion while in SI engine detonation occurs near the end of combustion.
In Cl engines knocking tendency increases with
Increase in compression ratio reduces the delay period as it raises both temperature and density, which decreases the knocking tendency of Cl engine.
In Cl engines by increasing inlet air pressure the knocking tendency
In Cl engines the delay period is affected by
Match List-I with List-Il and select the correct answer using the codes given below the lists:
A. Cetane number
B. Approach and range
D. dh = cpdT, even when pressure varies
1. Ideal gas
2. Van der Waals gas
3. SI engines
4. Cl engines
5. Cooling towers
6. Heat exchangers
A B C D
(a) 1 2 3 4
(b) 1 2 4 5
(c) 4 5 2 1
(d) 5 4 1 2
Which one of the following action(s) increase(s) the knocking tendency in the SI engine?
Increasing CR will increases temperature and reduction in engine speed slows down flame speed travel.
Which of the following feature(s) is/are used in the combustion chamber design to reduce SI engine knock?
The spark plug should be located closed to exhaust valve. So that it is not in the end region otherwise detonation will occur.
Which of the following factor(s) increase(s) the tendency for knocking in Cl engine?
A diesel engine is usually more efficient than a spark ignition engine because
For same compression ratio and the same heat supplied, Otto cycle is most efficient and diesel cycle is least efficient.
In practice, however, the compression ratio of the Diesel engine ranges between 14 and 25 whereas that of the Otto engine between 6 and 12. Due to higher compression ratio diesel engine is more efficient than petrol.