A Vertical Kerosene Oil Engine is a single or multi-cylinder internal combustion engine with the cylinder mounted upright, burning kerosene (paraffin) injected into a heated vaporiser or hot bulb where compression and residual heat ignite the charge. Typical units ran at 250-600 RPM and produced 2-50 brake horsepower, with thermal efficiencies around 12-18%. The vertical layout saves floor space versus horizontal oil engines, which is why fishing boats, lighthouses, and pump houses adopted them — the Hornsby-Akroyd vertical and the Lister CS vertical variants powered remote farms and coastal vessels for decades before diesel displaced them.
Vertical Kerosene Oil Engine Interactive Calculator
Vary bore, stroke, IMEP, RPM, and mechanical efficiency to see brake horsepower, indicated horsepower, torque, and shaft power update with an animated hot-bulb engine diagram.
Equation Used
This calculator estimates flywheel brake horsepower for a vertical kerosene oil engine from indicated mean effective pressure, cylinder swept volume, engine speed, and mechanical efficiency. For a four-stroke single-cylinder engine, only one power stroke occurs every two revolutions, so RPM/2 is used in the power calculation.
- Single-cylinder four-stroke engine with one power stroke every two crank revolutions.
- IMEP is entered as average indicated mean effective pressure in psi.
- Mechanical efficiency converts indicated horsepower to brake horsepower at the flywheel.
- Bore and stroke are in inches; stroke is converted to feet inside the calculation.
The Vertical Kerosene Oil Engine in Action
The engine starts cold on gasoline (or with a blowlamp warming the vaporiser bulb) because kerosene will not vaporise reliably at ambient temperatures. Once the hot bulb or vaporiser chamber reaches roughly 300-400 °C, you switch the fuel feed to kerosene and the engine self-sustains — residual combustion heat keeps the bulb hot, the bulb vaporises the next charge, and compression alone (around 3-5:1 in true hot-bulb engines, 8-12:1 in later vaporiser-injection types) raises the mixture to ignition temperature. This two-fuel start is what separates an oil engine from a true diesel: the diesel relies purely on compression heat, the kerosene oil engine cheats by keeping a glowing surface inside the chamber.
Vertical orientation matters more than it sounds. The trunk piston runs in a cylinder that drains oil cleanly back to the sump under gravity, the connecting rod loads the crankshaft symmetrically, and the cylinder head sits where you can reach the vaporiser, fuel pump, and governor without crawling underneath. Slow-speed governing — typically a flyball governor cutting fuel rather than throttling air — keeps RPM within ±5% of the set point under varying load. If the governor sticks open, RPM can climb 30-40% before the engine self-limits on poor combustion, and the bulb can melt or the wrist pin can hammer. If the governor sticks shut, the engine simply stalls, no harm done.
The failure modes are predictable. Carbon builds up inside the vaporiser if the fuel-air ratio runs rich, which insulates the bulb and cools combustion until the engine misfires every other stroke — you hear it as an uneven exhaust beat. Water in the kerosene quenches the bulb and the engine quits cold. Worn intake valves let compression bleed past, dropping peak pressure below the threshold the bulb needs to fire reliably. The fix in all three cases is operator-level work: decarb the bulb with a wire brush every 200-400 hours, water-trap the fuel line, and re-lap the valves on a schedule. None of this is glamorous but it is why these engines lasted 50+ years in the field.
Key Components
- Vaporiser / Hot Bulb: Cast-iron chamber bolted to the cylinder head, heated externally for cold start and kept hot by combustion residual heat. Operating surface temperature 300-450 °C. Wall thickness typically 6-10 mm — thinner cracks from thermal shock, thicker takes too long to come up to temperature on start-up.
- Fuel Injector / Spray Nozzle: Low-pressure mechanical pump (50-300 psi, far below diesel injection pressure) sprays metered kerosene onto the hot bulb wall. Nozzle orifice 0.4-0.8 mm. If the orifice carbons up the spray pattern collapses to a stream and combustion goes rough.
- Trunk Piston: Cast iron, 3-5 compression rings plus 1-2 oil control rings. Piston-to-bore clearance typically 0.10-0.15 mm cold. Vertical orientation lets oil drain back to the sump under gravity, reducing ring wear versus horizontal layouts.
- Flyball Governor: Centrifugal weights on the camshaft pull a sleeve that closes the fuel rack at over-speed. Set point typically 350 or 500 RPM with ±5% droop. If the linkage gums up with old oil the governor lags and RPM hunts ±15%.
- Crankshaft and Flywheel: Single-throw or multi-throw forged steel crank. Heavy cast-iron flywheel — often 30-50% of total engine mass — smooths the firing pulses of a single-cylinder engine where only one power stroke per two revolutions delivers torque.
- Two-Fuel Tank System: Small gasoline tank (1-2 L) for cold starts, main kerosene tank (10-50 L) for running. Three-way cock at the carburettor or fuel pump switches feed once the bulb glows.
Who Uses the Vertical Kerosene Oil Engine
These engines filled the niche between steam plants (too big, too much labour) and electric motors (no grid available) from roughly 1895 to 1955. Anywhere you needed a few horsepower of reliable mechanical work in a remote location, a vertical kerosene engine was the default answer. Kerosene was cheap, available globally, safer to store than gasoline, and the engines tolerated dirty fuel that would destroy a diesel injector.
- Marine — Coastal Fishing: The Kelvin Poppet vertical kerosene engine powered Scottish and Irish ring-net fishing boats from the 1900s through the 1950s, with 7-30 BHP units driving direct-coupled propellers.
- Agriculture — Farm Power: The Lister CS vertical (cold-start) engine ran water pumps, threshing machines, and chaff cutters on Australian and Indian farms — the 5/1 model at 5 BHP and 600 RPM became the default farm prime mover in the British Empire.
- Lighthouse and Buoy Service: Trinity House lighthouse stations used vertical Hornsby-Akroyd kerosene engines to drive air compressors for fog signal diaphones, sized 8-15 BHP, running on grade-1 kerosene stored in lighthouse tankage.
- Rural Electrification: Pre-grid farms in the American Midwest ran 32 V Delco-Light plants — small vertical kerosene gensets, 1-3 kW, charging lead-acid battery banks for house lighting.
- Mining — Dewatering: Cornish tin mines and Australian gold workings used vertical kerosene engines to drive piston and centrifugal pumps lifting groundwater, typically 15-50 BHP units running 24/7 with manned oiling rounds every 2 hours.
- Industrial — Workshop Lineshaft: Small machine shops and sawmills belt-drove overhead lineshafts from a single vertical kerosene engine, typically a Crossley or Ruston Hornsby 10-25 BHP unit.
The Formula Behind the Vertical Kerosene Oil Engine
Brake power is the number you actually care about — what the engine delivers at the flywheel after friction losses. The formula below ties indicated mean effective pressure, swept volume, and speed to brake horsepower through a mechanical efficiency factor. At the low end of the operating range — call it 250 RPM on a Lister CS-class engine — you get smooth, low-stress running but the engine produces maybe 60% of rated power because IMEP drops slightly at low speed. At the rated speed (typically 500-600 RPM) you hit the design sweet spot where vaporiser temperature, intake breathing, and governor stability all align. Push past rated speed and friction losses climb fast, mechanical efficiency falls from ~80% toward 70%, and the bulb can over-heat from the higher firing rate.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Pbrake | Brake power at the flywheel | kW | BHP |
| Pmi | Indicated mean effective pressure in the cylinder | kPa | psi |
| L | Stroke length | m | in |
| A | Piston cross-sectional area | m² | in² |
| N | Engine speed | RPM | RPM |
| n | Power strokes per revolution (½ for 4-stroke, 1 for 2-stroke) | — | — |
| ηmech | Mechanical efficiency (friction losses) | — | — |
Worked Example: Vertical Kerosene Oil Engine in a restored Petter M-type vertical kerosene engine
You are commissioning a restored 1938 Petter M-type single-cylinder vertical kerosene engine at a working museum in Devon, England. The engine drives a belt-coupled cider press auger during weekend demonstrations. Bore is 114 mm (4.5 in), stroke is 140 mm (5.5 in), rated speed is 600 RPM, and the workshop manual quotes IMEP of 550 kPa at full load. You want to verify expected brake power across the realistic demonstration speed range so you can size the press auger drive correctly without stalling the engine in front of visitors.
Given
- Bore = 114 mm
- Stroke (L) = 140 mm
- Pmi = 550 kPa
- N (rated) = 600 RPM
- n (4-stroke) = 0.5 —
- ηmech = 0.80 —
Solution
Step 1 — compute piston area from bore:
Step 2 — compute brake power at rated 600 RPM (the nominal design point):
This matches the Petter M-type factory rating of roughly 4 BHP and tells you the auger drive needs to absorb no more than that at peak cider-pressing torque, otherwise the governor will run wide open and RPM will sag.
Step 3 — at the low end of the demonstration range, 350 RPM (the engine will idle here between press cycles), IMEP drops slightly because vaporiser heat soak is lower; assume Pmi falls to 480 kPa:
At 350 RPM the engine is barely working — you would hear long pauses between firing strokes and the flywheel would carry most of the inertia. Visitors love this because the exhaust beat is dramatically slow, but you cannot extract real work here.
Step 4 — at the high end, 700 RPM (above rated, governor still in range), mechanical efficiency drops because piston friction climbs roughly with speed squared; assume ηmech falls to 0.72:
You gain almost nothing in brake power above rated speed — the IMEP gain is eaten by friction losses — and the vaporiser bulb starts running hotter than its design temperature. Hold it there for 20 minutes and you risk warping the bulb wall or pre-igniting the charge.
Result
The Petter M-type delivers a nominal 3. 14 kW (4.2 BHP) at its rated 600 RPM — exactly enough to drive a small cider press auger with the flywheel smoothing out the press-cycle torque pulses. Across the operating range the engine produces 2.1 BHP at 350 RPM idle, 4.2 BHP at 600 RPM rated, and a marginal 4.4 BHP at 700 RPM where you start cooking the bulb — so 600 RPM is genuinely the sweet spot, not just the spec-sheet number. If your dyno reading comes in 20-25% below the predicted 4.2 BHP, the most likely causes are: (1) a partially carbonned-up spray nozzle collapsing the kerosene spray pattern and dropping IMEP, (2) a leaking exhaust valve seat — easy to spot because compression test will read below 350 kPa cold — or (3) a slipping flat belt on the dyno coupling, which steals 5-15% before you ever see it on the gauge.
When to Use a Vertical Kerosene Oil Engine and When Not To
The vertical kerosene oil engine competed against three other prime movers in its era and against modern small diesels today. Pick the right one based on fuel availability, duty cycle, and how much hands-on operator skill you have on site.
| Property | Vertical Kerosene Oil Engine | Small Stationary Diesel | Vertical Steam Engine |
|---|---|---|---|
| Typical operating speed | 250-600 RPM | 1500-3000 RPM | 100-300 RPM |
| Thermal efficiency | 12-18% | 30-40% | 5-10% |
| Cold start time | 10-20 min (bulb pre-heat) | 5-30 sec | 30-60 min (boiler raise) |
| Fuel tolerance | Excellent — runs on dirty kerosene, used cooking oil, paraffin | Poor — needs clean filtered diesel | Excellent — coal, wood, oil, anything that burns |
| Service life between major overhauls | 20,000-50,000 hours | 8,000-15,000 hours | 30,000+ hours (boiler limited) |
| Mass per BHP | 80-150 kg/BHP | 5-15 kg/BHP | 150-300 kg/BHP |
| Operator skill required | Moderate — fuel switching, bulb temp judgment | Low — start key, walk away | High — boiler licensing required |
| Best application fit | Remote stationary duty, marine auxiliary, heritage demo | Modern gensets, mobile equipment | Heritage rail, historic vessels, biomass plants |
Frequently Asked Questions About Vertical Kerosene Oil Engine
The vaporiser bulb has not reached operating temperature. Gasoline ignites on compression heat alone in a 4-5:1 engine, but kerosene needs a glowing surface at 300 °C minimum to vaporise reliably. If you switch fuels too early the kerosene hits a cool bulb, condenses to liquid on the wall, and quenches whatever flame was there.
Run the engine on gasoline under light load for at least 8-10 minutes before switching. Touch the outside of the bulb housing with a wet finger — if water flashes off instantly, the bulb is hot enough. If it merely sizzles, give it another 3 minutes.
If the demonstration audience expects to see a slow, audible exhaust beat with a heavy flywheel doing visible work, the kerosene engine wins — that is the show. If you need reliable unattended operation and minutes-long start-up is unacceptable, the diesel wins.
The kerosene engine also tolerates fuel contamination that would destroy a Bosch-style diesel injector — relevant if the museum stores fuel for months between events. The diesel will deliver more BHP per kg and far better fuel economy, but those metrics rarely matter to a heritage operator running 40 hours a year.
Governor hunting on a kerosene engine is almost always linkage friction, not governor weight wear. The flyball-to-fuel-rack linkage sits in a hot, oily environment for decades and the pivot pins gum up with oxidised oil. The governor calls for more fuel, the linkage lags, then over-corrects, then lags again — you hear it as a slow oscillation.
Pull the linkage, clean every pivot with solvent, re-pin where the holes are oval, and use a light oil (ISO 32) on reassembly. If hunting persists after that, check the governor spring rate — a tired spring lets the weights swing too far for a given speed change.
That magnitude of shortfall almost always points to vaporiser geometry rather than the bottom end. If a previous owner machined the bulb wall thinner during a decarb, or if a replacement bulb was cast to a different internal volume, the effective compression ratio drops and IMEP falls hard. A 10% bulb volume increase can knock 25-30% off brake power.
Measure the bulb internal volume with a graduated cylinder of light oil. Compare against the manufacturer's drawing if you have it. Also check the kerosene grade — modern paraffin sometimes has a lower calorific value than 1940s kerosene, costing you another 5-8%.
Yes for diesel — many vertical kerosene engines were dual-rated for distillate fuels, and diesel actually has a slightly higher calorific value, giving 3-5% more power. The vaporiser handles it without modification. Used vegetable oil works too but only if filtered to 10 microns and only when the engine is fully warmed up; it cokes the nozzle faster than kerosene.
What you cannot run is gasoline alone for extended periods. The hot bulb causes severe pre-ignition with gasoline and will hammer the wrist pin and big-end bearings within an hour. Gasoline is for cold start only.
Looser than you would expect. A typical vertical kerosene engine runs 0.10-0.15 mm cold piston clearance on a 100 mm bore — roughly twice what a modern automotive engine uses. The slow speed means piston velocity is low, oil film stays thick, and thermal expansion of the heavy cast-iron piston demands the extra room.
Tighten it below 0.08 mm and the piston will scuff within 30 minutes of warm-up because the cast-iron skirt expands faster than the cast-iron bore at the top of the cylinder where the bulb dumps heat. Open it past 0.20 mm and you lose compression and the bulb misfires under load.
References & Further Reading
- Wikipedia contributors. Hot bulb engine. Wikipedia
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
