JNTUH B.Tech IV AUTOMOBILE ENGINEERING Previous Question Paper (September - 2022 - R16)

Lubricating systems in internal combustion engines are primarily classified into: Mist lubrication, Wet sump lubrication, Dry sump lubrication, and Pressure lubrication. Among these, the splash lubrication system is commonly used in small, low-speed engines.

In the splash lubrication system, the engine oil is stored in an oil sump at the bottom of the crankcase. A dipper or scoop is attached to the big end of the connecting rod. As the crankshaft rotates, the dipper dips into the oil trough and splashes the oil in the form of a spray or mist onto the cylinder walls, piston rings, and bearings. This mist provides the necessary lubrication for the moving parts. The oil then drains back into the sump to be reused. This system is simple and inexpensive but is generally unsuitable for high-speed or high-load engines due to inconsistent lubrication distribution.

Multi-Point Fuel Injection (MPFI) is a system where fuel is injected into the intake port of each cylinder individually, rather than at a single central point. Advantages include: uniform air-fuel ratio distribution among cylinders, improved volumetric efficiency, better throttle response, reduced exhaust emissions, and easier cold starting.

The principle of working involves an electronic control unit (ECU) that receives signals from various sensors (such as throttle position, mass airflow, and crankshaft position). Based on these inputs, the ECU calculates the precise amount of fuel required and triggers the fuel injectors located at each intake port to spray fuel at the optimal timing. This ensures that each cylinder receives the exact mixture needed for the current engine load and speed.

MPFI is widely applied in modern spark-ignition (S.I.) engines, particularly in passenger cars and light commercial vehicles, to meet stringent emission norms and enhance fuel economy.