First diesel engine 1897 — ignition by compression (3D)
About this app
Rudolf Diesel's test engine in section: a compression-ratio slider shows temperature and pressure at the end of compression until the injected fuel ignites by itself. Comparison with the Otto engine in p-V and T-s diagrams, efficiencies, measurements from 1897.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
Self-ignition through compression
A diesel engine draws in only air and squeezes it hard. The air heats up without any heat being added: for ideal, adiabatic compression T₂ = T₁ · ε^(κ−1). At a compression ratio of 13, air at 20 °C reaches about 545 °C. When fuel is introduced now, it ignites by itself, so no spark plug is needed. Rudolf Diesel patented the process in 1893; his first working engine was measured at Maschinenfabrik Augsburg in 1897 and reached an efficiency of 26.2 percent. The original is on display in the Deutsches Museum in Munich.
What the app shows
An own 3D reconstruction of the 1897 engine: A-shaped frame, crosshead, flywheel, a bottle of blast air and a cylinder cut open at the front with a 250 mm bore and 400 mm stroke. The air in the cylinder changes colour with its temperature, round displays show temperature and pressure from the ideal calculation, and the fuel is blown in as a jet. One panel calculates end temperature, end pressure and ignition delay; another compares the Otto and diesel cycles in p-V and T-s diagrams with their ideal efficiencies.
Things to try
Drag the compression-ratio slider from 4 to 24 and watch when the fuel ignites: at ε = 8 it stays a mist, at ε = 13 it burns. Set the intake air to −10 °C and the limit rises, the cold-start problem. Switch to the Otto process: a ready mixture compressed that much knocks. The diagram panel shows why the diesel wins despite constant-pressure combustion, because it may compress much more.
Frequently asked questions
- Why does a diesel engine not need a spark plug?
- It compresses pure air so strongly that the air becomes several hundred degrees hot, about 545 °C ideally at ε = 13. The fuel introduced shortly before top dead centre ignites by itself in this hot air. The glow plugs of modern diesels only help with cold starts.
- Why does a petrol engine compress less than a diesel?
- A petrol engine compresses a ready fuel–air mixture. If it is compressed too much, it ignites by itself before the spark and the engine knocks. That is why petrol engines long used compression ratios of about 4 to 10, diesels about 14 to over 20.
- What is the difference between the constant-volume and constant-pressure cycle?
- In the ideal Otto cycle heat is added at constant volume, so the pressure jumps straight up in the p-V diagram. In the ideal diesel cycle the fuel burns while the piston is already moving down, at roughly constant pressure. At the same ε the ideal Otto cycle is better; the diesel wins through higher compression.
- What can I try in this app?
- You set the compression ratio and the intake air temperature, switch between diesel and Otto, step through the four strokes and compare both cycles in p-V and T-s diagrams. The AI tutor can also demonstrate self-ignition.
Subject: Physics experiments (Deutsches Museum)
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