Automotive Lubrication, Injection Systems & Engine Performance
Objectives of Lubrication
Primary Objectives
- Reduce friction – minimizes resistance between moving parts.
- Minimize wear – protects surfaces from damage and extends component life.
- Dissipate heat – carries away heat generated due to friction.
- Form a protective film – prevents direct metal-to-metal contact.
- Enhance efficiency – reduces energy losses during operation.
Secondary Objectives
- Prevent corrosion – acts as a barrier against moisture and chemicals.
- Seal contaminants out – helps in sealing gaps to block dust and debris.
- Clean the system – flushes away particles and impurities.
- Reduce noise and vibration – provides cushioning in moving parts.
Telescopic Shock Absorber: Construction and Working
Construction
A telescopic shock absorber consists of the following main parts:
- Cylinder or outer tube: holds hydraulic oil and provides structural support.
- Piston and piston rod: moves up and down within the cylinder.
- Oil reservoir: contains oil for damping.
- Valves (compression and rebound): control the flow of oil to dampen vibrations.
- Seals and dust covers: prevent leakage and entry of dust.
Working
- Compression: when the vehicle wheel moves over a bump, the suspension compresses and the piston rod moves downward.
- Oil is pushed through the compression valve, creating hydraulic resistance and absorbing energy.
- Rebound: during rebound (when the spring expands), the piston moves upward, forcing oil through the rebound valve and again resisting motion.
- This damping action controls spring oscillations, ensuring a smooth ride.
Difference Between Injection Systems
Individual Pump and Nozzle System
Each cylinder has its own high-pressure pump and injector. Fuel is pressurized individually and injected mechanically. Offers precise control but is complex and costly; used mainly in large engines.
Unit Injector System
The pump and injector are combined into a single unit per cylinder. Fuel is pressurized by a camshaft-driven plunger and electronically controlled. Provides high injection pressure and precise control.
Common Rail System
A single high-pressure pump feeds a common rail supplying fuel to all injectors. Injectors are electronically controlled, allowing flexible and precise injection timing. It is efficient but expensive and complex.
Distributor System
Uses a single rotary pump to pressurize and distribute fuel to all cylinders. It is mechanically or partially electronically controlled. Simple and compact, but offers lower injection pressure and less precision.
P–V Diagram: Naturally Aspirated vs Supercharged
Diagram Overview
Both engines follow the Otto cycle (or the Diesel cycle for diesels), showing four main processes:
- 1–2: Isentropic compression
- 2–3: Constant-volume heat addition
- 3–4: Isentropic expansion
- 4–1: Constant-volume heat rejection
The difference lies in the initial pressure and volume (point 1).
Naturally Aspirated Engine
- Intake air is drawn in at atmospheric pressure (~1 bar).
- The P–V diagram starts at a lower pressure.
- Smaller area under the curve, meaning less work output.
Supercharged Engine
- Uses a compressor (driven mechanically or by exhaust gases in turbocharging) to increase intake air pressure.
- Starting pressure (point 1) is higher than atmospheric.
- The P–V diagram shifts upward and slightly right.
- Larger area under the curve indicates more power output due to more air–fuel mixture burned.
Effects of Under-Cooling and Over-Cooling
Under-Cooling (Insufficient Cooling)
- Engine overheats.
- Causes knocking and reduced efficiency.
- Increases wear and risk of seizure.
Over-Cooling (Operating Below Optimal Temperature)
- Engine runs below optimal temperature.
- Poor fuel combustion and low efficiency.
- Increases fuel consumption and emissions.
Why Fins Are on the Air Side, Not the Water Side
- Air has lower heat transfer capacity than water.
- Fins increase surface area to enhance heat transfer in air-cooled systems.
- Water already has high thermal conductivity, so fins are unnecessary on the water side.
Viscosity, Service Ratings, and Multi-Grade Oils
Viscosity refers to a lubricant’s resistance to flow. It determines how easily oil moves through engine parts and provides protection. Thicker oils (high viscosity) flow slower and are better for high temperatures, while thinner oils (low viscosity) flow faster and are suitable for cold conditions. Viscosity is commonly measured using SAE (Society of Automotive Engineers) grades, such as SAE 10W-30.
Service ratings are classifications provided by organizations like the API (American Petroleum Institute). These ratings (e.g., API SN, API CK-4) indicate the oil’s performance in various engine types and conditions. “S” series oils are for gasoline engines, while “C” series are for diesel engines.
Multi-grade oils are lubricants that perform effectively across a wide temperature range. They combine the benefits of both low and high viscosity oils. For example, SAE 10W-30 behaves like SAE 10W in cold weather for easy starting and like SAE 30 at high temperatures to ensure protection. These oils reduce the need to change oil with seasonal temperature changes.
Why Heavy Vehicles Need More Than Three Gears
- Heavy vehicles carry large loads, requiring high torque at low speeds for starting and climbing.
- More gears provide better torque multiplication to move the load efficiently.
- Higher gears allow smooth acceleration and fuel efficiency at cruising speeds.
- Fewer gears would cause engine strain, poor fuel economy, and difficulty in varied terrain.
Alternative Fuel and Energy Options for Future Automobiles
- Electricity (Battery Electric Vehicles – BEVs): powered by rechargeable batteries and electric motors.
- Hydrogen fuel cells: generate electricity through a chemical reaction between hydrogen and oxygen.
- Biofuels: derived from organic matter (e.g., ethanol, biodiesel) and used in modified internal combustion engines.
- Compressed Natural Gas (CNG): a cleaner fossil fuel alternative for petrol or diesel engines.
- Synthetic fuels (e-fuels): produced from renewable electricity and carbon dioxide, compatible with existing engines.
Use of Hydrogen in Future Automobiles
Hydrogen is used in fuel cell vehicles (FCVs), where it reacts with oxygen in a fuel cell stack to produce electricity, with water vapor as the only emission. Hydrogen vehicles offer fast refueling (similar to gasoline) and longer driving ranges compared to battery EVs. They are especially suitable for heavy-duty vehicles and long-distance travel, contributing to reduced greenhouse gas emissions and supporting a cleaner energy future.
Compression Ratio Limits in Spark-Ignition Engines
The highest compression ratio that can be used in a spark-ignition (S.I.) engine is limited by the detonation characteristics of the fuel because detonation, or knocking, occurs when the air–fuel mixture auto-ignites prematurely due to excessive pressure and temperature during compression. As the compression ratio increases, the temperature of the mixture also rises, increasing the risk of knocking. This can lead to engine damage, reduced efficiency, and poor performance. The resistance of a fuel to knocking is measured by its octane number; higher-octane fuels can withstand higher compression without detonating. Therefore, the compression ratio in an S.I. engine must be kept within the safe limits defined by the knocking resistance of the fuel being used.
Best Spark Plug Position in the Combustion Chamber
The most favorable position for a spark plug in a combustion chamber is at the center of the cylinder head. This central location ensures uniform flame propagation in all directions, resulting in faster and more complete combustion. It reduces the distance the flame has to travel, minimizing the chances of detonation and ensuring better thermal efficiency. Additionally, central positioning helps reduce emissions, improves fuel economy, and ensures smoother engine operation. Therefore, placing the spark plug at the center is ideal for optimal performance.