Auto-Sector Interview Preparation

Intake, Compression, Power (combustion/expansion), and Exhaust. The piston draws in the air-fuel mixture, compresses it, the spark/heat ignites it to push the piston down producing power, and finally the burnt gases are expelled.

SOHC (Single Overhead Camshaft) uses one camshaft per cylinder bank to operate both intake and exhaust valves. DOHC (Dual Overhead Camshaft) uses two — one for intake, one for exhaust — enabling more valves per cylinder, higher RPM, and better breathing and performance.

A turbocharger uses energy from the exhaust gases to spin a turbine connected to a compressor. The compressor forces more air into the intake, allowing more fuel to be burned per cycle, which increases power output without increasing engine displacement.

Both force more air into the engine. A turbocharger is driven by exhaust gases (free energy but with some lag). A supercharger is driven mechanically by the crankshaft (instant response but consumes engine power). Turbos are more efficient; superchargers give more immediate boost.

Knocking is the premature/uncontrolled detonation of the air-fuel mixture before the spark plug fires, causing a metallic pinging sound. Causes include low-octane fuel, excessive compression, over-advanced ignition timing, carbon deposits, or engine overheating. It can damage pistons and bearings.

It maintains optimal operating temperature by removing excess heat. Coolant circulates through the engine block and cylinder head, absorbs heat, passes through the radiator where it's cooled by airflow (aided by the fan), and a thermostat regulates flow to keep temperature in the ideal range.

Compression ratio is the ratio of cylinder volume at bottom-dead-centre to top-dead-centre. Higher compression extracts more energy from fuel (better efficiency and power) but requires higher-octane fuel to avoid knocking. Petrol engines typically run 9:1–12:1; diesels 16:1–22:1.

A diesel engine compresses only air to a very high ratio, raising temperature enough to auto-ignite injected fuel (compression ignition) — no spark plug. A petrol engine compresses an air-fuel mixture ignited by a spark plug. Diesels have higher torque and efficiency; petrol engines rev higher and run smoother.

The flywheel stores rotational kinetic energy and smooths out the power pulses from individual combustion strokes, keeping the crankshaft rotating evenly between power strokes. It also provides the ring gear for the starter motor and a mounting surface for the clutch.

It reduces harmful exhaust emissions through catalytic reactions. Using precious metals (platinum, palladium, rhodium), it converts carbon monoxide to CO2, unburnt hydrocarbons to CO2 and water, and nitrogen oxides to nitrogen and oxygen.

Valve timing is the precise points in the cycle when intake/exhaust valves open and close. VVT adjusts this dynamically with engine speed and load — improving low-end torque, high-end power, fuel economy, and emissions simultaneously. Examples: Honda VTEC, Toyota VVT-i.

Torque is the rotational force the engine produces (how hard it can push, felt as pulling power). Horsepower is the rate of doing work — a function of torque and RPM (power = torque × RPM ÷ constant). Torque gets the load moving; horsepower determines top speed.

Throttle-body injection (one/two injectors at the throttle), multi-point/port injection (one injector per cylinder at the intake port), and direct injection (fuel sprayed directly into the combustion chamber for precise control, better efficiency and power). Modern engines often combine port and direct injection.

Oil lubricates moving parts, reduces friction and wear, cools, cleans (carries contaminants to the filter), and seals. Grade like 5W-30: '5W' is cold-start viscosity (lower = better cold flow), '30' is viscosity at operating temperature. Multigrade oils perform across temperature ranges.

The firing order is the sequence in which cylinders fire (e.g. 1-3-4-2 for many inline-4s). It's designed to balance the engine, minimise vibration, distribute load evenly on the crankshaft, and avoid consecutive firing of adjacent cylinders. Wrong firing order causes misfires and rough running.

Both are cylinder sleeves. A wet liner is in direct contact with coolant (better cooling, replaceable, used in heavy-duty engines). A dry liner is pressed into the block with no direct coolant contact (more rigid, used where the bore needs reinforcement or repair).

A manual transmission uses a clutch and driver-selected gears. An automatic uses a torque converter (fluid coupling) and planetary gearsets that shift automatically based on speed and load, controlled hydraulically/electronically. Variants include CVT (continuously variable) and DCT (dual-clutch).

A torque converter is a fluid coupling that transmits power from the engine to an automatic transmission while allowing the engine to idle when stopped. It also multiplies torque at low speeds via the stator, improving low-speed pulling power, and locks up at cruising speed for efficiency.

Causes: low coolant, faulty thermostat, failed water pump, blocked radiator, broken cooling fan, or a blown head gasket. Diagnose by checking coolant level and leaks, testing the thermostat, verifying fan operation, pressure-testing the system, and checking for combustion gases in the coolant.

BS6 is India's emission standard (aligned with Euro 6), mandatory from April 2020. It drastically cut permissible NOx, particulate matter, and hydrocarbons. Engines added technologies like selective catalytic reduction (SCR/AdBlue) for diesels, diesel particulate filters (DPF), better fuel injection, and OBD-II diagnostics.