Q.1.What is advantage And Disadvantage of CDI ?

Capacitive discharge ignition (CDI) system :

Advantages :

The advantages of CDI system are :

1. The capacitor in this system can store several thousands times more energy per unit of capacitance compared to that per unit inductance of the conventional TCI system. This permits a high output voltage even at high spark rates (speeds).
2. Due to the internal resistance being very small (about 50 Ω), faster voltage rise is obtainable and consequently the system is relatively insensitive to side tracking.
3. As in TCI system, the breaker points serve as a trigger only. This avoids frequent maintenance and increases life of the contact points.
4. As evident from Fig. 13.13, at low engine speeds in CDI systems low current is drawn from the battery and with increase in speed the current drawn also increases, unlike what happens in conventional or TCI system where high current is drawn at low speeds. This characteristic of CDI system increases the low speed efficiency and allows easier cold starting.

Disadvantages :

The main disadvantage of CDI system is very rapid discharging of capacitor leading to strong spark but of short duration of about 0.1 ms. This may cause ignition problems when operating with rich mixtures.

Q.2.What is advantage of Multigrade oils ?

Multigrade oils.

It is possible to develop an oil with more than one viscosity at different temperatures. Thus an oil may be in SAE-30 grade at 99°C and in the SAE-10 W grade at – 18°C, oils of this type are known as multigrade oils ; other possible grades are : 5 W/20, 20 W/20, 20 W/40.
Following are the “advantages” of multigrade oils :

1. No necessity to change the oil as per the ambient temperature.
2. Owing to ease of cranking at low ambient temperature the life of battery is extended.
3. Long engine life ; required viscosity is maintained under different operating temperatures.
4. Easy starting and short warming up period.
5. Reduced oil consumption.
6. Prolonged mileage between the decarbonisation.
7. Due to execellent thermal and oxidation stability of multigrade oils the engine parts are protected against rust, corrosion and wear.

Q.3.What is advantage And Disadvantage of Mist of Lubricantion system?

Advantages : Mist of Lubricantion system

1. System is simple.
2. Low cost (because no oil pump, filter etc. are required).>

Disadvantages :

1. Some lubrication oil will burn and cause heavy exhaust emissions and deposits on piston crown, ring grooves and exhaust port and thus hamper the good performance of the engine.
2. Since the lubricating oil comes in contact with acidic vapours produced during the combustion process, it rapidly loses its anti-corrosion properties resulting in corrosion damage of bearing.
3. The oil and fuel must be thoroughly mixed for effective lubrication. This requires either separate mixing prior to use or use of some additive to give the oil good mixing characteristics.
4. Owing to higher exhaust temperature and less efficient scavening the crankcase oil is diluted. In addition some lubricating oil burns in combustion chamber. This results in 5 to 15 per cent higher lubricant consumption for two stroke engine of similar size.
5. As there is no control over the lubricating oil, once introduced with fuel, most of the two stroke engines are over-oiled most of the time.

Q.4.What is advantage And Disadvantage of pressurised engine cooling over conventional thermo-syphon cooling system ?

Advantages of pressurised engine cooling over conventional thermo-syphon cooling system :

Following are the advantages of pressurised engine cooling over conventional thermo-syphon cooling system :

1. Effective and positive cooling of all parts. Local overheating is avoided.
2. It can take overload easily because as the engine speed increases the water circulation also increases, and same effective cooling can be maintained at all the speeds.
3. In thermo-syphon system, the radiator should be kept well above the
engine, to provide a height for natural circulation. There is no such requirement for pressurised forced pump system.
4. With pressurised system the coolant temperature is maintained higher. This reduces corrosion.
5. Smaller coolant passages can be used. This reduces weight and bulk of the engine.
6. No loss of water by boiling and evaporation.

Q.5.What is advantage And Disadvantage of Hyperbar turbochargering ?

Advantages : Hyperbar turbochargering

1. High power-to-weight ratio.
2. High brake mean effective pressure to the tune of 30 bar can be obtained (peak pressure limited to 140 bar).
3. Thermal loading-moderate.
4. Surge pre-operation (due to by pass control).
5. Good torque and acceleration available.

Disadvantages :

1. Due to low compression ratio, there is high fuel consumption over the entire range of operation.
2. System is complex.

Q.6.What is advantage and applications of dual-fuel engines ?

Advantages and applications of dual-fuel engines

Advantages :

1. A duel-fuel engine can run on either of the fuel and diesel requirement is hardly 5 percent if it runs on gas.
2. Reduced pollution.
3. It is preferred when cheap gas is easily available.
4. Owing to clean combustion in the engine the wear and tear of the engine as well as consumption of lubricating oil are reduced.
5. The engine’s utility is considerably increased due to the possibility of instantaneous change over from gas to diesel and vice-versa.
6. Best suited for low pressure liquified gas (LPG) which evaporates very easily.
7. Very attractive power generation system because of its greater flexibility of operation compared with conventional diesel engines.

Applications :

1. A typical use of duel-fuel engine is to produce synthetic gas (mixture of CO and H2) by burning CH4 and simultaneously developing power.
2. A lot of conventional fuel can be saved by using duel-fuel engines particularly for irrigation purposes.

Q.7. What is advantage And Disadvantage of Stratified Charge Engines ?

Advantages and Disadvantages of Stratified Charge Engines

The advantages and disadvantages of stratified charged engines are listed below :

Advantages :

1. Compact, lightweight design and good fuel economy.
2. Good part-load efficiency.
3. Exhibit multi-fuel capability.
4. The rich mixture near the spark plug and lean mixture near the piston surface provides cushioning to the explosive combustion.
5. Resist the knocking and provide smooth combustion resulting in smooth and quiet engine operation over the entire speed and load range.
6. Low level of exhaust emissions ; NOx is reduced considerably.
7. Usually no starting problem.
8. Can tolerate wide quality of fuels.
9. Can be manufactured by the existing technology.

Disadvantages :

1. For a given engine size, charge stratification results in reduced power.
2. These engines create high noise level at low load conditions.
3. More complex design to supply rich and lean mixture, and quantity is varied with load on the engine.
4. Higher weight than that of a conventional engine.
5. Unthrottled stratified charge engines emit high percentage of HC (due to either incomplete combustion of lean charge or occasional misfire of the charge at part load conditions.
6. Reliability is yet to be well established.
7. Higher manufacturing cost.