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Four Stroke Engine

Last Update:

09/06/2016

Introduction

Four stroke engines have powered automobiles around the world, ever since their invention more than a century ago. Despite the rise of electric cars, the four stroke engine still reigns supreme.

History

Inspired by Jean Joseph Etienne Lenoir’s work on two-stroke, coal-gas powered engines, Nicolaus Otto went on to develop a better internal combustion engine along with Eugen Langen.

  • They founded NA Otto and Cie in 1864 and moved operations to Deutz in Germany, and the company was renamed Deutz Gasmoterenfabrik AG. Gottlieb Daimler was appointed as a technical director and Wilhelm Maybach as head of engine design for the company.
  • The first engine that used compressed fuel-air mixture was produced in 1876. Daimler and Mayback left to form their own company - the Daimler Motoren Gesellschaft Co., and became famous for developing a high speed Otto cycle engine in 1883
  • By 1885 the company produced the Reitwagen engine using hot tube ignition running on Ligroin fuel. It was the world’s first four stroke internal combustion powered car. Later, Karl Benz produced his own version in 1886 claiming it to be the world’s first car. 

Nicolaus  Otto noticed that the Lenoir engine relied on differential in pressure to deliver power. He developed the first four stroke engine that compressed fuel-air mixture to drive the piston through the power explosion, which in turn, turned a crankshaft to transfer power to the flywheel. He also claims the credit for developing the carburetor and an electric ignition system in 1890.

Types

The most basic of four stroke engines has a single cylinder-single piston configuration with two valves. Manufacturers went on to develop and refine this basic configuration model that relied on petrol as the fuel. Petrol four stroke engines are being developed for over the century. The parallel twin was developed as an improvement on the single cylinder, using two pistons to double power strokes per crankshaft rotation, resulting in a smoother power balance and transfer.

  • Inline engine: This is the simplest with four or more cylinders in a row arranged in an engine block contributing to balance and less maintenance.
  • V-Type Engine: Two cylinder rows housing 2 or 4 pistons. Each engine opposes the other at an angle of 90 degrees, resulting in low center of gravity, better rigidity, higher compression ratios and more power, ideal for racing purposes.
  • Boxer or flat engine: In this design the two cylinder blocks are at 180 degree opposition to each other in the horizontal direction with the crankshaft in the center. This type of engine has a low center of gravity and offers better stability as well as cornering capabilities.
  • Wankel rotary engine: Strictly speaking, this is not the traditional piston-cylinder configuration since the crankshaft is stationary while the cylinder block rotates. The engine, however reproduces the four Otto-cycle strokes of intake, compression, power and exhaust but the similarity ends there. The engine has an oblong shaped combustion chamber and a lobed rotor forms pockets for the four cycles.
  • Diesel four-stroke engine: Rudolph Diesel developed a high compression engine using air-fuel mix sprayed into the engine and ignited by heat of compression. It uses a glow plug instead of spark plugs found in petrol engines. Diesel engines today use diesel as the fuel and have their own performance characteristics.

The basic four stroke engines gained further refinements by way of fuel injection, more valves and turbochargers to gain more power, better fuel consumption and reduced emissions.

Main Parts

  • A typical car engine has a large cast engine block that may have two, three, four or more cylinders.
  • Each cylinder has a piston. The piston has a gudgeon pin with a connecting rod.
  • The connecting rod is attached to the crankshaft.
  • The crankshaft is at the bottom and has a flywheel at one end and interfaces with the alternator and gearbox at the other end. A pulley also connects a timing belt to the overhead camshaft.
  • The camshafts drive inlet and exhaust valves. The inlet valves are connected to a manifold that draws in the fuel-air mixture from the carburetor and the exhaust valves connect through a manifold to the exhaust pipe.
  • Each cylinder has a seperate spark plug connected to a distributor and ignition system.

How It Works

  • Four stroke engines operate on the Otto cycle divided into 4 strokes.
  • The piston is positioned at the bottom of the cylinder and the inlet valve opens to let in fuel and air mixture from the carburetor.
  • In the second stroke the piston moves up the cylinder to compress the fuel-air mixture, forming the compression stroke.
  • The third stroke comprises of combustion of the fuel-air mixture resulting in an explosion that drives the piston to the bottom of the cylinder and the force is transferred from the connecting rod to the crankshaft to drive the gearbox. The up and down motion of the connecting rod is translated to rotatory motion by the crankshaft.
  • In the fourth stroke the inlet valve is closed and the exhaust valve opens as the piston moves up into the cylinder to drive out exhaust through the exhaust manifold.

 

Effectiveness and challenges

  • Four stroke engines are inherently more efficient than two stroke engines, achieving an efficiency figure of 30% over it.
  • The emission levels are also lower for four stroke engines. Noise levels are lower in comparison to turbine jet engines or two stroke engines.
  • There is flexibility in design which allows the engines for motorcycles and appliances can have a single piston smaller configuration while larger and more powerful vehicles can have multiple piston-cylinder configurations to deliver more torque.

However, there are challenges as well.  

  • Despite highly advanced engineering technologies, the basic limitations remain in that the engine relies on piston and cylinder that in turn rely on the fuel and its octane rating as well as oxygen content in air to achieve power output. Fuel injection, superchargers and turbochargers do try to maximize fuel efficiency and power output but the basic design’s limitation put a limit to how much can be achieved.
  • Pistons and valves wear out and result in reduced performance.

 

Maintenance Tips

Four stroke engines are computer controlled in modern cars. However, routine maintenance checks can be performed to ensure a healthy running engine with long life.  

  • Check spark plugs for fouling and keep them clean as well as keep the gap adjusted
  • Check carburetor and fuel flow lines to ensure there is no dirt or blockage
  • Check exhaust smoke that indicates wear and tear of pistons and carburetor performance.
  • Check valve train and set timings to adjust for valve seat and valve wear and tear as well as check for overhead camshaft wear.

Four stroke engines are the mainstay of cars and motorcycles,  as well as portable tools and small aircrafts. Hence, efforts for constant innovation in design and development are undertaken to focus on  improving reliability and fuel efficiency in the future.

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