engine designer Interview Questions and Answers

1. What are the fundamental differences between a four-stroke and a two-stroke engine?

   • Answer: A four-stroke engine completes its power cycle in four piston strokes (two revolutions of the crankshaft), involving intake, compression, power, and exhaust strokes. A two-stroke engine completes its power cycle in two piston strokes (one revolution of the crankshaft), combining intake and exhaust with compression and power in a single stroke. Two-strokes are generally simpler, lighter, and more powerful for their size but less fuel-efficient and produce more emissions.

2. Explain the Otto cycle and its efficiency limitations.

   • Answer: The Otto cycle is a thermodynamic cycle describing the functioning of a typical spark-ignition internal combustion engine. It consists of four processes: isentropic compression, constant-volume heat addition, isentropic expansion, and constant-volume heat rejection. Efficiency is limited by the compression ratio and the specific heat ratio of the working fluid. Higher compression ratios lead to higher efficiency but also risk engine knock. Heat loss to the cylinder walls also reduces efficiency.

3. Describe the Diesel cycle and how it differs from the Otto cycle.

   • Answer: The Diesel cycle is similar to the Otto cycle but differs in the method of heat addition. In the Diesel cycle, heat is added at constant pressure during the combustion process, while in the Otto cycle, heat is added at constant volume. This difference leads to higher thermal efficiency in Diesel engines at higher compression ratios, but also results in higher emissions of NOx and particulate matter.

4. What is engine knock and how can it be avoided?

   • Answer: Engine knock is the uncontrolled auto-ignition of the air-fuel mixture in the cylinder before the spark plug fires. It can lead to damage to the engine. It can be avoided by using higher octane fuel, optimizing the air-fuel mixture, using advanced ignition timing control, and employing knock sensors to detect and adjust engine parameters in real-time.

5. Explain the role of the crankshaft and connecting rod in an engine.

   • Answer: The crankshaft converts the reciprocating motion of the pistons into rotary motion, which drives the vehicle's wheels or other machinery. The connecting rod connects the piston to the crankshaft, transferring the force from the piston to the crankshaft.

6. What are the different types of engine cooling systems?

   • Answer: Common engine cooling systems include air cooling (using fins to dissipate heat), liquid cooling (using a coolant circulated through the engine and a radiator), and evaporative cooling (using a coolant that evaporates to absorb heat).

7. Explain the function of the lubrication system in an engine.

   • Answer: The lubrication system reduces friction between moving parts, preventing wear and tear. It also helps to cool engine components and remove contaminants.

8. What are the different types of fuel injection systems?

   • Answer: Common fuel injection systems include port fuel injection (PFI), direct fuel injection (DI), and throttle body injection (TBI). PFI injects fuel into the intake manifold, DI injects fuel directly into the combustion chamber, and TBI injects fuel into the throttle body.

9. Describe the function of a turbocharger and a supercharger.

   • Answer: Both turbochargers and superchargers increase the air intake into the engine, leading to increased power output. A turbocharger uses exhaust gas energy to drive a turbine, which compresses the intake air. A supercharger is mechanically driven by the engine itself.

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