Steam engines powered the first industrial revolution, but they needed boilers, water and hours to raise steam. From the late nineteenth century, a new family of engines burned fuel inside the engine itself. The petrol engine made the motor car practical, the diesel engine took over ships, locomotives, trucks, mining and farm machinery, and the gas turbine made jet flight and modern power stations possible. Today, electric drives and batteries are displacing combustion engines in many uses.
None of these technologies simply replaced the others. Each won where its strengths matched the work: light weight and low cost for cars, efficiency and torque for heavy sustained loads, power-to-weight and continuous operation for aircraft and power generation. Understanding why helps engineers and managers choose power sources well, whether specifying a generator for a remote site, a fleet of vehicles or a production machine.
This article traces the development of internal combustion engines, from early gas engines and Otto’s four-stroke cycle to Diesel’s compression ignition engine and the gas turbine, explains in plain terms why efficiency depends on compression and temperature, and draws out lessons about matching technology to the duty, the limits set by materials, emissions and the transition to electric power. It is general information for engineers, operations managers and business leaders.
From gas engines to the four-stroke cycle
Inventors had experimented with engines burning fuel inside a cylinder since the seventeenth century. In 1860, Étienne Lenoir in France built a practical gas engine, but it was inefficient because it did not compress its fuel and air mixture before burning it.
In 1876, Nikolaus Otto in Germany perfected the four-stroke cycle that most petrol engines still use:
- Induction: the piston moves down, drawing in a mixture of fuel and air.
- Compression: the piston moves up, compressing the mixture.
- Combustion and expansion: a spark ignites the mixture, and the expanding gases push the piston down, doing work.
- Exhaust: the piston moves up, pushing out the burned gases.
Compressing the mixture before burning it was the key to better efficiency.
The motor car
In 1886, Karl Benz patented a three-wheeled vehicle powered by a light, fast-running petrol engine, generally regarded as the first practical motor car. Gottlieb Daimler and Wilhelm Maybach developed fast petrol engines at about the same time. Early cars established features that persisted: water cooling, electric ignition, a carburettor to mix fuel and air, and a transmission to match engine speed to road speed.
Mass production, through vehicles such as the Ford Model T from 1908, made cars affordable. Its simple, durable, easily repaired engine suited buyers in places with few roads and little servicing support. Over the following century, the basic piston engine stayed the same, while almost everything around it improved: overhead valves, fuel injection, turbocharging, electronic controls and exhaust treatment.
Diesel: an engine designed from a thermodynamic argument
Rudolf Diesel set out to build an engine that approached the theoretical efficiency limits described by thermodynamics. Diesel’s patents date from 1892, and by 1897 a test engine demonstrated efficiency higher than any other heat engine of its time.
The difference from a petrol engine is how combustion starts. A diesel engine compresses air alone, to a much higher ratio, which heats it above the temperature at which fuel ignites. Fuel is then sprayed in, and it ignites without a spark.
Why compression ratio matters
For engines of this type, efficiency rises as the compression ratio rises, because compressing more before combustion allows more expansion afterwards, turning more of the fuel’s energy into work rather than exhaust heat.
A petrol engine compresses a mixture of fuel and air, so if it compresses too much, the mixture ignites on its own before the spark, a damaging effect called knock. That limits petrol engines to compression ratios of roughly 9:1 to 12:1. A diesel engine compresses only air, so it has no such limit, and typically runs at roughly 14:1 to 22:1. The diesel’s efficiency advantage comes mainly from being allowed to compress harder.
What diesel’s efficiency cost
Higher pressures need heavier, stronger engines, and early diesels were large and expensive. Their efficiency and strong torque at low speed suited heavy, sustained work. Diesel engines powered ships from the early twentieth century, and diesel-electric locomotives, in which a diesel engine drives a generator powering electric traction motors, replaced steam locomotives in many countries from the 1930s to the 1960s. Diesel became dominant in trucks, buses, mining equipment, farm machinery and stationary generators, including in Australia, where diesel powers much of the mining and agricultural sectors and many remote communities and sites.
Petrol and diesel compared
| Characteristic | Petrol, spark ignition | Diesel, compression ignition |
|---|---|---|
| Ignition | Spark in a fuel and air mixture | Fuel injected into hot compressed air |
| Compression ratio | Limited by knock | Set high to reach ignition temperature |
| Efficiency | Lower, especially at part load | Higher, especially at part load |
| Weight and cost | Lighter and cheaper | Heavier and more expensive |
| Torque | Good at higher speeds | Strong at low speeds |
| Typical emissions concerns | Carbon monoxide, unburnt fuel, nitrogen oxides | Nitrogen oxides and particulate matter |
| Best suited to | Light vehicles, intermittent duty | Heavy, sustained loads |
Neither is better in general. The duty decides, together with fuel prices, emissions rules and the support available locally.
The gas turbine: continuous combustion
A gas turbine does the work of a piston engine continuously rather than in separate strokes. A compressor squeezes air continuously, fuel burns continuously in a combustion chamber, and the hot gases expand through a turbine that drives the compressor, with surplus energy available as thrust or shaft power.
Frank Whittle in Britain and Hans von Ohain in Germany independently developed jet engines in the late 1930s, and the first jet-powered flight took place in Germany in 1939. Gas turbines have high power for their weight and run smoothly, which made them ideal for aircraft. They also became central to electricity generation: in combined cycle power stations, the hot exhaust from a gas turbine raises steam to drive a steam turbine, reaching overall efficiencies of around 60%, much higher than either alone.
Efficiency is limited by materials
For any heat engine, the theoretical maximum efficiency depends on the temperatures at which heat is received and rejected: the hotter the heat source, the higher the possible efficiency. Gas turbines therefore improve by running hotter, but turbine blades must survive extreme temperatures while spinning at high speed. Progress has depended on nickel-based superalloys, single-crystal blades, ceramic coatings and internal cooling passages. The limit is set by materials, not by thermodynamic theory.
How the modern engine improved
The basic architecture of piston engines has changed little in a century: pistons, valves, liquid cooling and hydrocarbon fuel. What changed is everything around it:
- Turbocharging uses exhaust energy to drive a compressor that forces more air into the engine, raising power from a given size and improving efficiency.
- Fuel injection replaced carburettors, and electronic control now meters fuel precisely for each cylinder and cycle, enabling effective exhaust treatment.
- High-pressure common rail injection in diesels made them quieter, cleaner and more responsive.
- Better breathing, through overhead camshafts, multiple valves per cylinder and variable valve timing, improved performance across a wide speed range.
- Electronic engine management controls ignition, fuel, boost and emissions systems together, and records faults for diagnosis.
Each of these improvements was incremental, but together they multiplied the power available from an engine of a given size and cut emissions dramatically, another example of a mature technology improving through many steps rather than one breakthrough.
Keeping engines reliable in service
Engines in industrial service last longest when maintained to their duty. Practical points include servicing by operating hours as well as calendar time; oil analysis, testing samples for wear metals, contamination and degradation to detect problems before failure; keeping air intakes, fuel and cooling systems clean; and avoiding long periods of light loading. Diesel generators that run lightly loaded for long periods can suffer wet stacking, where unburned fuel and soot accumulate in the exhaust, reducing performance and increasing maintenance. Periodic running at higher load, or right-sizing the generator, prevents it.
Emissions and the move to electric power
Combustion engines produce carbon dioxide and other pollutants. Through the late twentieth century, regulations on vehicle and engine emissions drove catalytic converters, particulate filters, exhaust gas recirculation and selective catalytic reduction. Concern about climate change is now driving a broader shift.
Electric motors are far more efficient than combustion engines at converting energy into motion, are quiet and produce no local emissions, and batteries have become dramatically cheaper. Electric drives are replacing combustion engines first where duty cycles suit them: urban vehicles, forklifts, short-haul transport, mining equipment in some applications and stationary power supported by solar generation and batteries. Diesel remains important where energy density, refuelling time and long operating hours matter, and alternatives such as hydrogen and renewable fuels are being developed for those duties. As always, the duty decides.
Lessons for engineering and business
Match the technology to the duty
Petrol, diesel, gas turbine and electric power each won where their strengths suited the work. When choosing a power source, start with the duty: load profile, running hours, part-load operation, weight, refuelling and maintenance.
Understand the governing constraint
Diesel’s advantage came from removing the knock limit on compression; gas turbines advance by overcoming material temperature limits. Knowing what actually limits a technology shows where improvement is possible.
Design from first principles where it helps
Diesel designed the engine from a thermodynamic argument rather than improving an existing machine, and it outperformed everything else. Starting from fundamentals can reveal options that incremental improvement misses.
Part load matters
Engines are often most efficient near their rated load. Oversized generators and engines running lightly loaded waste fuel and can suffer maintenance problems. Sizing to the real duty is as important as choosing the technology. The selecting electric motors and drives article covers the same principle for electric motors.
Regulation and energy prices change the answer
Emissions rules, fuel prices and the falling cost of batteries and solar power have changed which technology is best for many duties. Review power choices periodically rather than treating them as permanent.
A worked example
This is an illustrative example. The figures are assumptions. A remote processing site is powered by a diesel generator rated at 100 kW, with an average load of about 40 kW around the clock. Running at low load, the generator uses about 0.35 litres of fuel per kilowatt-hour.
Current cost. The site uses about 40 kW × 8,760 hours, or 350,400 kWh, a year. At 0.35 litres per kilowatt-hour, that needs about 122,600 litres of diesel. At an assumed delivered price of $2.00 a litre, fuel costs about $245,000 a year, before maintenance, which is higher than necessary because the generator runs lightly loaded.
Option. An energy consultant proposes adding solar panels and a battery, keeping the diesel generator for night-time and cloudy periods. Modelling suggests the hybrid system could reduce diesel use by about 60%, saving about $147,000 a year in fuel, for an assumed installed cost of about $600,000, a simple payback of about four years. The generator would also run less often, and closer to its efficient load when it does.
Decision. The business commissions a detailed study using measured load data and local solar data, confirms reliability arrangements and proceeds in stages. As with the history of engines, the choice is not about one technology being better in general, but about which mix best suits the duty, the energy prices and the reliability required. The buying for the whole life of equipment article explains how to compare such options on whole-of-life cost.
Applying these lessons in an Australian business
- Define the duty before choosing engines, generators or vehicles.
- Size equipment to the real load, avoiding lightly loaded operation.
- Compare whole-of-life costs, including fuel, maintenance and emissions compliance.
- Understand what limits each option, such as part-load efficiency, weight or refuelling.
- Review power choices as fuel prices, regulations and technology costs change.
- Consider hybrid solutions where duty cycles vary.
- Maintain to the duty, using operating hours and condition checks such as oil analysis.
Questions worth considering
- What is the actual load profile and running pattern of our equipment?
- Are our engines and generators sized for the work they really do?
- How would rising fuel prices or tighter emissions rules change our costs?
- Which of our duties now suit electric or hybrid power?
- When did we last review the power choices behind our operations?
- How do we monitor engine condition, and are we servicing to actual operating hours?
Bringing it together
Internal combustion engines transformed transport, industry and power generation because each type matched particular duties: petrol for light, intermittent use; diesel for heavy, sustained loads; gas turbines for power-to-weight and continuous generation. Their histories show that efficiency depends on compression and temperature, that materials often set the real limits and that emissions, prices and new technologies keep changing the best choice. For businesses, the lasting lesson is to start from the duty and choose, size and review power sources accordingly.
Source: KEVOS editorial notes, drawing on an earlier KEVOS engineering history series on the internal combustion engine, compression ignition, diesel-electric traction and the gas turbine, together with established histories of technology. The worked example uses assumed figures and is illustrative. This article is general information.
