Lesson 13 Internal Combustion Engine The Diesel Part A

Contents Working Principle of a Diesel Engine Operation of systems Two stroke engines Four stroke engines Comparison between the Two-Stroke Engine and the Four-Stroke Engine Gas Exchange Process Other Supporting Systems

Working Principle of a Diesel Engine The diesel engine is a type of internal combustion engine that ignites the fuel by injecting it into hot, high-pressure air in a combustion chamber.

Working Principle of a Diesel Engine In common with all internal combustion engines the diesel engine operates with a fixed sequence of events, which may be achieved either in four strokes or two, a stroke being the travel of the piston between its extreme points. Each stroke is accomplished in half a revolution of the crankshaft.

Working Principle of a Diesel Engine Increased pressure of combustion gases acts on piston -> converted to rotary motion Can be 2 or 4 stroke engines 2-stroke: 1 power stroke per 1 crankshaft rev. 4-stroke: 1 power stroke per 2 crankshaft rev.

Operation Engine stroke A stroke is a single traverse of the cylinder by the piston (from TDC to BDC) 1 revolution of crankshaft = 2 strokes of piston

Working Principle of a Diesel Engine V s +V c V 1 e= = V c V2 p x D 2 V c = x S 4 pk= p 1 x e n n=polytrope exponent 1.35 p 1 =pressure at the beginning of the compression absolute pressure t k =T 1 xe n T 1 =temp at the beginning of the compression in Kelvin degree ( rec. temp )

Four-Stroke Diesel Engine The four-stroke cycle is completed in four strokes of the piston, or two revolutions of the crankshaft. In order to operate this cycle the engine requires a mechanism to open and close the inlet and exhaust valves.

Four-Stroke Diesel Engine

Intake stroke Intake valve open, exhaust valve shut Piston travels from TDC to BDC Air drawn in Compression stroke Intake and exhaust valves shut Piston travels from BDC to TDC Temperature and pressure of air increase

Four-Stroke Diesel Engine Power stroke Intake and exhaust valves shut Fuel injected into cylinder and ignites Piston forced from TDC to BDC Exhaust stroke Intake valve shut, exhaust valve open Piston moves from BDC to TDC Combustion gases expelled

Two-Stroke Diesel Engine The two-stroke cycle is completed in two strokes of the piston or one revolution of the crankshaft. In order to operate this cycle where each event is accomplished in a very short time, the engine requires a number of special arrangements.

Two-Stroke Diesel Engine First, the fresh air must be forced in under pressure. The incoming air is used to clean out or scavenge the exhaust gases and then to fill or charge the space with fresh air. Instead of valves, holes, known as ‘ports’, are used which are opened and closed by the sides of the piston as it moves.

Two-Stroke Diesel Engine One power stroke every crankshaft revolution Uses pressurized air to simultaneously supply new air and expel combustion gases Scavenging Exhaust valve open, inlet port exposed Pressurized air enters, expels combustion gases Piston near BDC

Two-Stroke Diesel Engine

Two-Stroke Diesel Engine Compression Intake and exhaust valves shut Piston travels from BDC to TDC Temperature and pressure of air increase Power stroke Intake and exhaust valves shut Fuel injected into cylinder and ignites Piston forced from TDC to BDC

Two-Stroke Diesel Engine 1 st Stroke (Compression) Piston at BDC Scavenge Ports and Exhaust Valve Open Scavenge air flows into the cylinder and presses the exhaust gases through the exhaust valve to the turbocharger. Piston Moves Upwards: Scavenge ports are being closed Exhaust valve shuts, compression begins

Two-Stroke Diesel Engine 2nd Stroke (Ignition – Combustion – Expansion – Exhaustion – Scavenging) Just Before TDC Fuel is injected into the cylinder, Fuel Ignites in the compressed and heated air = ignition, with ignition combustion begins Gases Expands and Press Piston Downwards (working stroke) The exhaust valve opens, exhaust gases flow out if the cylinder to the turbo. Scavenge ports are being uncovered by the downward moving piston, scavenge air flows into the cylinder and presses the exhaust gases out through the exhaust valve to the the turbocharger.

Comparison Two-stroke advantages Higher power to weight ratio Less complicated valve train Four-stroke advantages More efficient burning process As size increases, power-to-weight ratio improves

Gas Exchange Process

Gas Exchange Process Uniflow Scavenging

Gas Exchange Process Cross FlowLoop Flow

Mean Effective Pressure MEP is the value referring to the constant pressure which would have to exist in a cylinder during power stroke to produce the same power at the flywheel.

Diesel Fuel System Fuel System Fuel Supply System 燃油供给系统 Fuel Injection System 燃油喷射系统 Injection Nozzles Injection Pump Filters Transfer Pump Fuel Tank

Diesel Fuel System

Diesel Fuel System Density: 密度 Viscosity: 粘度 Flash point: 闪点 measure the delivery quantity by weight adjust centrifuges temperatures for treatment & injection for safety Combustion: Combustion product: Maintenance: viscosity 粘度 cetane number 十六烷值 calorific value 发热值 sulphur 硫 carbon residue 残碳 ash 灰分 flash point 闪点 setting point 凝点 viscosity 粘度 specific gravity 比重 water content 水分 mechanical impurities 机械杂质

Diesel Fuel System

Fuel Injection System the amount of fuel 定量 at the right moment 定时 in a suitable condition 定质 a metered amount of fuel according to the load on the engine timing mechanism to atomize the fuel

Cooling Water System Fresh Water Cooling System 淡水冷却系统 Sea Water Cooling System 海水冷却系统

Cooling Water System Fresh Water Cooling System To cool: cylinder jackets and covers exhaust valves water cooled turbochargers

Cooling Water System Fresh Water Cooling System Cooling water pumps: 冷却水泵 Fresh water cooler: 淡水冷却器 Corrosion prevention: 防腐蚀 independently driven & controlled in duplicate (one as standby) with pressure relief valves & alarms cooled with sea water pressure of fresh water higher corrosion inhibitors 抑蚀剂 alkaline agents 碱剂 chemical additives 化学添加剂

Cooling Water System Sea Water Cooling System Usual arrangement Central cooling system individual coolers for lubricating oil, jacket water, and piston cooling one large sea water circulated cooler individual coolers circulated by fresh water ☆ Advantage ： Corrosion problems are greatly reduced.

Cooling Water System

Words & Expressions internal a. 内在的 ignite v. 发火、点火 mechanism n. 机械装置、机构 scavenge v. 扫气 timing n. 定时 cylinder n. 汽缸 combustion n. 燃烧 exhaust vi. 排气 cycle 周期, 循环 inlet 进口, 入口

Assignments What is a diesel engine? What is the four-stroke cycle? What is the two-stroke cycle? What special arrangements does the two- stroke cycle require? Describe the operation between two fuel injections.