Marine Diesel Engine Simulator
Slow-Speed Two-Stroke Ship Engine in 2D & 3D — Animate • Learn • Practice • Quiz
Display Controls
⚙ Engine geometry & rating, valve timing, scavenge air
The scavenge ports are opened and closed by the piston itself, so their timing follows from the port height and is symmetric about BDC. The exhaust valve times are free. Compression starts when the valve closes, so EVC sets the effective compression ratio. The rod ratio L/r = 4 is a typical crosshead value, not a maker’s figure.
Σ Live equations — values substituted from the current engine
📋 Cycle points — pressure, volume and temperature at each event
🌀 Gas exchange — injection, valve and port events of one revolution
💡 What-if coach — insights from the current operating point
1 Overview
The Marine Diesel Engine Simulator runs the slow-speed two-stroke crosshead diesel that drives most large ships. In 2D one cylinder unit is cut across the engine at true scale, with a person on the operating platform for size: bedplate and crankshaft, connecting rod, the crosshead sliding in its guides, the piston rod through the stuffing box, the piston in the liner with its scavenge ports, the cylinder cover with the fuel injectors and the exhaust valve, and the scavenge air and exhaust receivers. In 3D the whole engine stands in its engine room.
The propeller sets the load, a governor sets the fuel, and every cylinder runs a limited-pressure cycle. The readouts give power, speed, torque, mean effective pressure, the maximum and compression pressures, the scavenge air, SFOC, brake thermal efficiency, fuel per day, exhaust temperature, air excess and the firing order.
2 Running the Engine
- Telegraph — the bridge’s orders: Stop, Dead slow (30 % of MCR speed), Slow (45 %), Half (60 %), Full (80 %) and Sea speed (100 %). The Engine speed slider sets any speed from 25 to 105 %.
- Heavy running raises the propeller curve (a fouled hull, bad weather or a deep-loaded ship): the same speed then needs more power and torque.
- Engine picks one of three real engines (published bore, stroke, MCR speed and power per cylinder) or Custom. Cylinders (above the canvas) sets 5 to 14 cylinders; Follow cylinder chooses the unit shown.
- Play/Pause runs the engine; Animation speed 1 is real time, which for a slow-speed engine is slow enough to watch. Step turns the followed cylinder to its next event, the arrow keys nudge the crank by 5°, and a press on the crank lets you turn it by hand.
- Units — SI (bar, kW, °C, mm, MN·m, g/kWh) or Imperial (psi, bhp, °F, in, lbf·ft, lb/hp·h). Fuel per day stays in metric tonnes, as bunkers are bought and logged in tonnes everywhere.
- The advanced panel holds the geometry and rating, the exhaust valve timing and maximum firing pressure, the scavenge air pressure and temperature, and the share of fuel heat the cycle receives.
3 The Five Diagrams
- P–V — the cylinder’s cycle with the trapping (EVC), TDC, end of combustion, EVO and port-opening points, and the scavenge air pressure.
- Indicator — pressure against crank angle round TDC, the “draw card” engineers take on board, with the compression-only curve that gives pcomp and the firing-pressure limit.
- Timing — one revolution: fuel injection, expansion, the exhaust valve open, the ports open and compression, with every event angle.
- Load — the engine load diagram on logarithmic axes: the propeller curve, heavy running, the MCR point, the torque and speed limits and the operating point.
- Torque — the gas torque on the crankshaft over one revolution for one cylinder and the whole engine, with the mean.
2D and 3D, at the left of the strip above the canvas, switch views. The page opens in 3D on a computer or tablet and in 2D on a phone; your last choice is remembered for that kind of device, and a link ending ?view=2d or ?view=3d opens that view. In 3D drag to turn the engine, Ctrl + scroll or pinch to zoom, right-drag or Shift-drag to pan, double-click to reset, and click a part to read what it does. Cutaway opens the followed unit down its middle so its running gear shows; Platforms shows the gratings, railings and the engineer for scale; Labels names the main parts.
4 Calculations, Learning Panels and Export
The calculator icon works the operating point step by step: volumes, the propeller’s power demand, scavenge air and trapped charge, compression, the fuel the governor injects, limited-pressure combustion, work, mean effective pressure, power, torque and SFOC. The learning panels show the live equations, the cycle points, the gas-exchange events and a what-if coach. Explain walks through one revolution in seven steps. Right-click (long-press on touch) the canvas for a menu. CSV exports the setup, the results and a 1° sweep of volume, pressure, temperature and torque; PNG saves the canvas.
5 Explore, Practice and Quiz
Explore has sixteen cards in four groups: Basics, Crosshead & valves, Thermodynamics, and Ship & propeller. Practice draws from ten problem types (swept volume, firing interval, power from mean effective pressure, shaft torque, the propeller law, efficiency from SFOC, fuel per day, mean piston speed, effective compression ratio and firing frequency). Quiz asks six questions from a pool of twenty, with the options shuffled each time.
6 What the Model Assumes
Each cylinder runs a limited-pressure (dual) cycle: polytropic compression (n = 1.37) from the exhaust valve closing, heat added at constant volume up to the maximum firing pressure and then at constant pressure, polytropic expansion (n = 1.30) to the exhaust valve opening, and an exponential blow-down. A set share of the fuel energy reaches the gas; the rest is lost to the cooling water. Friction is a mean pressure that rises with speed. The scavenge air pressure follows a fit to typical shop-test curves rather than a turbocharger model, and auxiliary blowers run below 35 % load. The propeller absorbs power as the cube of speed. The firing order is the crank arrangement with the smallest free first- and second-order moments; real makers also weigh torsional vibration. Inertia forces, the turbocharger’s own thermodynamics, reversing and starting air are not modelled.
How a Marine Diesel Engine Works — Two-Stroke Ship Engine Simulator
Almost every large container ship, tanker and bulk carrier is driven by a slow-speed two-stroke crosshead diesel engine. It is coupled straight to the propeller shaft with no gearbox, turns at only 60–120 rpm, and is the most efficient heat engine in everyday use: about 50 % of the energy in its fuel reaches the propeller. This simulator runs one at true scale, from the crankshaft to the exhaust valve, with the propeller, the governor and the turbocharger setting the operating point.
Marine Diesel Engine Parts
- Bedplate and A-frames — the bedplate carries the main bearings of the crankshaft; the A-frame columns above it carry the crosshead guides.
- Crankshaft — one crank throw per cylinder, spaced 360/n degrees apart, with a thrust bearing at the aft end that passes the propeller’s push into the hull.
- Connecting rod and crosshead — the connecting rod runs from the crank pin to the crosshead pin. The crosshead slides between guides, which take the side thrust.
- Piston rod and stuffing box — a straight rod from the crosshead to the piston, passing through a diaphragm that separates the scavenge air space from the crankcase.
- Piston, liner and scavenge ports — the liner has a ring of angled ports near its bottom that the piston uncovers near BDC.
- Cylinder cover, fuel injectors and exhaust valve — two or three injectors per cylinder, and one large exhaust valve opened by a hydraulic actuator and closed by an air spring.
- Turbocharger, air cooler and receivers — exhaust gas drives the turbocharger; the compressed air is cooled and fed to the scavenge air receiver along the engine.
The Two-Stroke Cycle and Uniflow Scavenging
A two-stroke engine completes its cycle in one revolution. Near TDC fuel is injected into air compressed to well over 100 bar and ignites by itself. The gas drives the piston down. At about 110° after TDC the exhaust valve opens and the gas blows down into the exhaust receiver. At about 140° the piston uncovers the scavenge ports and air from the scavenge receiver swirls up the cylinder, pushing the rest of the gas out through the valve. Because the air flows one way, from the ports at the bottom to the valve at the top, this is called uniflow scavenging. The piston covers the ports again as it rises, and when the exhaust valve closes compression begins.
Because compression only starts when the valve closes, the effective compression ratio is lower than the geometric one. In the simulator’s G95ME-C the geometric ratio is 21 : 1 but the effective ratio is about 13 : 1, giving a compression pressure of about 145 bar at full load. Electronically controlled engines move the valve closing to raise the compression pressure at part load.
Worked Example — Power of the MAN B&W G95ME-C9
The G95ME-C9 has a bore of 950 mm and a stroke of 3 460 mm, so each cylinder sweeps (π/4) × 0.95² × 3.46 = 2.453 m³. At its rated 80 rpm and a brake mean effective pressure of 21.0 bar, one cylinder delivers 21.0×10⁵ × 2.453 × 80/60 = 6 867 kW; the published rating of 6 870 kW per cylinder is the same figure with the MEP quoted to one decimal. A two-stroke fires every revolution, so there is no factor of ½ as in a four-stroke. An 8-cylinder engine makes 54 960 kW and puts a torque of about 6.6 MN·m on the propeller shaft. At an SFOC of 166 g/kWh it burns about 219 tonnes of fuel a day.
The Propeller Law and Slow Steaming
A fixed-pitch propeller absorbs power roughly as the cube of its speed, P = PMCR(N/NMCR)³. At 80 % speed the engine needs only 51 % of its rated power, which is why ships save so much fuel by slowing down. A fouled hull, bad weather or a deep-loaded ship makes the propeller “heavy”: the engine must then give more torque at the same speed, and the load diagram shows how close it comes to its torque limit.
Who Uses This Simulator?
Marine engineering cadets and STCW students learning the main engine before they meet one in an engine room, mechanical engineering students studying IC engines, the two-stroke cycle and mean effective pressure, instructors who want to show uniflow scavenging and the crosshead without a cutaway engine, and anyone curious about how the world’s biggest piston engines move a ship.
Frequently Asked Questions
What engine is used in large ships?
Most large cargo ships, tankers and container ships are driven by a slow-speed two-stroke crosshead diesel engine coupled directly to the propeller shaft, with no gearbox. It runs at about 60 to 120 rpm and turns about half the energy in its fuel into work at the shaft, which makes it the most efficient heat engine in everyday use.
Why are ship engines two-stroke?
A two-stroke engine fires every cylinder once per revolution, so at the low speed a large propeller needs it delivers twice the power of a four-stroke of the same size. With uniflow scavenging, a turbocharger and a crosshead it also burns heavy fuel oil efficiently and runs for tens of thousands of hours between overhauls.
What is uniflow scavenging?
Near the bottom of the stroke the piston uncovers a ring of ports round the lower end of the cylinder liner. Air from the scavenge air receiver swirls in through the ports and up the cylinder, pushing the burnt gas out through a single exhaust valve in the cylinder cover. The air flows one way only, from bottom to top.
What is a crosshead in a marine engine?
The crosshead is a block at the bottom of the piston rod that slides between guides in the engine frame. The connecting rod is pinned to it, so the side thrust of the rod is taken by the guides instead of by the piston and cylinder liner, which then wear far less.
Explore Related Simulators
- Four Stroke Engine Simulator — the car and truck diesel and petrol engine, with the Otto and Diesel cycles in 3D.
- Two Stroke Engine Simulator — the small petrol two-stroke with crankcase scavenging and loop-scavenged ports.
- Steam Engine Simulator — the reciprocating engine that drove ships before the diesel.
- Gas Turbine Simulator — the Brayton cycle, used in warships and LNG carriers.
- Slider-Crank Mechanism — the linkage the crosshead follows.
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