Basic Automobile Engineering — Exercise Solutions
Key Concepts Quick Recap
| Term | Definition |
|---|
| IC Engine | Internal Combustion Engine: fuel burns inside cylinder |
| TDC | Top Dead Centre: piston at highest point |
| BDC | Bottom Dead Centre: piston at lowest point |
| Stroke | Distance piston travels from TDC to BDC (or vice versa) |
| Bore | Diameter of cylinder |
| Compression ratio | Volume at BDC / Volume at TDC |
| Torque | Rotational force; Nm; diesel engines have higher torque |
| Power (BHP/kW) | Rate of doing work |
| Chassis | Frame and running gear of vehicle (excluding body) |
| Suspension | Connects wheels to chassis; absorbs shocks |
I. Choose the Best Answer (MCQs)
1. In a four-stroke engine, the power stroke occurs in which stroke? (a) First (b) Second (c) Third (d) Fourth
Answer(c) Third Four strokes in order: 1st = Suction, 2nd = Compression, 3rd = Power (combustion), 4th = Exhaust. Power is generated only in the 3rd stroke; crankshaft momentum carries through the other three.
2. The function of the carburetor in a petrol engine is: (a) Ignite the fuel (b) Mix fuel and air in proper ratio (c) Cool the engine (d) Store fuel
Answer(b) Mix fuel and air in proper ratio Carburetor: mixes petrol and air in approximately 1:14.7 (stoichiometric ratio) by weight. Modern vehicles use Electronic Fuel Injection (EFI) instead.
3. Diesel engines use which ignition system? (a) Spark ignition (b) Compression ignition (c) Surface ignition (d) No ignition system
Answer(b) Compression ignition Diesel engine: no spark plug; air is compressed to high pressure and temperature (>250°C); diesel fuel injected → auto-ignites. Called CI (Compression Ignition) engine.
4. The purpose of the clutch in a vehicle is: (a) Change wheel direction (b) Engage and disengage the engine from the transmission/gearbox (c) Slow down the vehicle (d) Steer the vehicle
Answer(b) Engage and disengage the engine from the transmission/gearbox Clutch: allows smooth engagement/disengagement of engine power to gearbox → enables gear changing without stopping the engine.
5. Disc brakes are preferred over drum brakes because: (a) Disc brakes are cheaper (b) Disc brakes have better heat dissipation and consistent braking performance (c) Drum brakes are less efficient (d) Disc brakes require no maintenance
Answer(b) Disc brakes have better heat dissipation and consistent braking performance Disc brakes: open air cooling; consistent stopping power (no brake fade); easy inspection; preferred for front wheels of cars. Drum brakes: enclosed; prone to brake fade; cheaper; still used on rear wheels of some vehicles.
6. The gear ratio is defined as: (a) Engine speed / Vehicle speed (b) Speed of input shaft / Speed of output shaft (c) Engine power / Vehicle weight (d) Torque × Speed
Answer(b) Speed of input shaft / Speed of output shaft Gear ratio = input RPM / output RPM. Lower gear ratio → more torque, less speed. Higher gear ratio → more speed, less torque.
7. ABS (Anti-lock Braking System) prevents: (a) Brakes from working (b) Wheel lockup during sudden braking, allowing steering control (c) Engine from stopping (d) Gearbox from shifting
Answer(b) Wheel lockup during sudden braking, allowing steering control ABS: sensors detect wheel lockup → pulses brake pressure → wheels don't lock → tyres maintain grip with road → driver can steer even during hard braking. Significantly reduces stopping distance on wet roads.
II. Short Answer Questions
Q1. Describe the major components of an IC engine.
Answer
| Component | Function |
|---|
| Cylinder block | Main body; houses cylinders |
| Piston | Reciprocates in cylinder; transmits combustion force |
| Connecting rod | Converts reciprocating motion of piston to rotating motion of crankshaft |
| Crankshaft | Converts linear motion to rotary motion; power output |
| Camshaft | Controls opening and closing of valves (driven by crankshaft via timing chain/belt) |
| Valves | Inlet (fuel-air in) and exhaust (burnt gases out) |
| Spark plug | Ignites fuel-air mixture (petrol engine only) |
| Fuel injector | Sprays fuel into cylinder (diesel and modern petrol engines) |
| Flywheel | Stores energy, smooths output, assists gear changes |
| Cylinder head | Seals top of cylinder; houses valves, spark plug |
Q2. What are the types of transmission systems in vehicles?
Answer
Manual transmission (MT):
- Driver changes gears via clutch pedal + gear lever.
- Types: sliding mesh (old), constant mesh, synchromesh (modern).
- Better fuel efficiency, driver control.
Automatic transmission (AT):
- Torque converter replaces clutch; planetary gearset; gear changes automatically.
- More convenient; preferred in traffic.
CVT (Continuously Variable Transmission):
- Infinite gear ratios between low and high; no fixed gears.
- Smooth acceleration; good fuel economy.
AMT (Automated Manual Transmission):
- Manual gearbox with automated clutch and gear actuation.
- Budget-friendly; India: Maruti Alto K10 AMT.
Exam Checklist
- Four-stroke petrol: Suction → Compression → Power → Exhaust.
- SI engine (petrol): spark plug; CR 8-12:1. CI engine (diesel): compression ignition; CR 14-22:1.
- Carburetor: mixes fuel + air (1:14.7); modern engines use EFI.
- Clutch: engages/disengages engine from gearbox.
- Disc brakes: better heat dissipation; preferred for front wheels.
- ABS: prevents wheel lockup; maintains steering control during hard braking.
- Gear ratio = input RPM / output RPM; lower gear = more torque.
