The single most common question we hear from first-time buyers of model and small turbojet engines is simple: what do I actually put in the tank? The short answer is clean kerosene — usually Jet A-1 — mixed with a small, precisely measured amount of approved synthetic turbine oil. The longer answer involves oil ratios, fuel quality, low-temperature behavior and a few fuels (notably gasoline) that should never be used. This guide consolidates the published requirements of the major model-turbine manufacturers for distributors, fleet operators and end users.
Virtually all modern model turbojets — engines in the few-kilogram-force to roughly 40 kgf class from manufacturers such as SWIWIN, JetCat and KingTech — are designed to run on kerosene-grade fuel containing a small percentage of synthetic turbine lubricating oil. The mixture performs two jobs at once:
That second point is why fuel and lubrication cannot be treated separately on a model jet. Run kerosene without oil, even briefly, and the bearings run dry. Run the wrong oil and the deposits, coking or inadequate film strength can produce the same result more slowly.
The published oil percentages from the major manufacturers cluster around 3%–5% by volume, but the exact figure is engine- and oil-specific, and manufacturers occasionally update their recommendations:
For a new engine or an unfamiliar batch of oil, 5% (50 ml of oil per liter of fuel) is the conservative default supported by every major manufacturer's published range. Measure with a graduated container, mix before filling, and never eyeball the ratio. Reduced ratios such as 3% are appropriate only where the specific engine manual and the specific oil both support them.
Model-turbine manufacturers approve synthetic turbine oils of the type used in full-size gas-turbine engines, typically qualified against the U.S. military specification MIL-PRF-23699 (formerly MIL-L-23699) or the civilian standard AS5780. These are ester-based synthetic oils formulated for thermal and oxidation stability at turbine operating temperatures. Commonly cited examples include:
Manufacturer approvals are not interchangeable. KingTech's manuals, for example, explicitly state that AeroShell Turbine Oil 500 is not recommended for its engines and list the approved oils (such as Mobil Jet Oil 254 and several model-industry turbine oils) by name. Two-stroke outboard oil, motorcycle oil, automotive engine oil and other general-purpose lubricants are not turbine oils: they can form carbon deposits on bearings and turbine wheels and their use voids warranty coverage across the industry. Always cross-check both the engine manual's approved-oil list and the oil product's qualification statement.
"Kerosene" covers several distinct products. The table below summarizes how the commonly available options apply to model turbojets; again, the engine manual has the final word.
| Fuel | Can it be used? | Notes |
|---|---|---|
| Jet A-1 aviation turbine kerosene, ASTM D1655 |
Preferred | The standard international aviation kerosene. Freezing point max −47 °C; contains a static-dissipator additive and strict quality control for water and particulates. The safest first choice wherever it is available. |
| Jet A ASTM D1655 |
Yes | Nearly identical to Jet A-1 but with a freezing point of −40 °C. Mainly supplied in the United States. Mix with oil in the same way; winter operators should note the higher freezing point. |
| 1-K kerosene ASTM D3699 |
Yes | Low-sulfur, low-aromatic heating/lighting kerosene — the usual "burner kerosene" at hardware and fuel stores. SWIWIN and JetCat manuals accept it. Buy clear, water-free, reputable fuel; cheaper grades vary in cleanliness. |
| RP-3 / No. 3 jet fuel GB 6537 (China) |
Yes | Chinese aviation turbine kerosene, broadly equivalent to Jet A-1. The reference fuel specified for engines such as our XX400WP. |
| No. 2 diesel / road diesel ASTM D975 |
Conditional | Accepted for ground-test and some flight use by SWIWIN, JetCat and KingTech, which note it is often cleaner and more water-tolerant than hardware kerosene. Trade-offs: lower lubricity (raise oil %), heavier odor/smoke, and wax gelling around −10 to −15 °C unless winterized. Not the first choice for cold-weather flight. |
| Gasoline / petrol including avgas and mogas |
Never | No model-turbine manufacturer approves gasoline. Far lower flash point (−43 °C vs 38 °C+ for kerosene) makes leaks and hot restarts a flash-fire/explosion hazard; volatility also causes vapor-lock and unstable combustion. Using it voids the warranty and creates a serious personal-safety risk. |
Kerosene and diesel are distillate fuels: at normal temperatures they do not form ignitable vapor-air mixtures readily, which is why a kerosene puddle is difficult to light with a spark. Gasoline is blended to vaporize aggressively — its vapors are heavier than air, invisibly pool around the engine and ignite from a tiny spark, hot exhaust or a failed restart. Gasoline also vaporizes in fuel lines and pumps (vapor lock), producing uncontrollable acceleration or flameout. The combination of fire hazard, poor combustion behavior and zero manufacturer approval makes it non-negotiable: gasoline in any form — automotive gasoline, avgas or small-engine fuel — must never be used in a kerosene-burning model turbojet.
Contamination does more day-to-day damage than any single bad fuel choice. Micro-turbine fuel systems pass mixture through small orifices and a fuel filter into an engine whose tolerances are measured in thousandths of an inch. The manufacturer guidance is consistent:
A properly run model turbine is a predictable piece of machinery; almost all serious fuel-related incidents trace to ground handling rather than the engine. The manufacturers' safety notes converge on a short list:
Low temperatures create two distinct problems. First, fuel itself can approach its limits: Jet A-1 is controlled to a −47 °C freezing point, while Jet A stops at −40 °C and ordinary No. 2 diesel begins to cloud and gel at roughly −10 to −15 °C, waxing filters and starving the engine. In winter conditions, use Jet A-1 or a treated winter-grade/arctic diesel — not summer road diesel. Second, batteries lose capacity in the cold, starter performance drops and ECU start routines may need longer preheat. Keep start batteries warm, expect longer cooldown between starts in the open, and re-check filter condition after any cold-weather flameout, since ice or wax is the usual culprit rather than the engine itself.
The failure modes follow predictably from the chemistry:
In every documented case, the manufacturer warranty covers defects in materials and workmanship — not damage traceable to fuel, oil or handling that departs from the manual. For distributors, this makes the fuel specification worth documenting at the point of sale: an end user who starts with the right fuel is an end user whose warranty claim, if one ever comes, stays valid.
The fuel-mixed-with-oil rule applies to small model turbines whose bearings are lubricated solely by the fuel passing through them. Larger small gas-turbine engines often use a separate lubrication system with its own oil tank and pump, and then run on straight aviation kerosene. For example, the XX400WP — a 40 kgf-class engine for industrial UAV and target platforms — specifies RP-3 aviation kerosene (GB 6537) as fuel and carries an independent 4050 synthetic-oil lubrication system with its own oil tank. If you are moving up from RC-scale engines, do not assume the 5% mixing habit applies: check the engine's fuel-system description first. Our 400kgf-class turbojet guide walks through the operational differences at that scale.
No. Model turbojets have no independent oil system; the synthetic turbine oil mixed into the fuel is what lubricates the high-speed bearings. Running straight kerosene — even for a short test — will overheat and destroy the bearings and typically wreck the engine.
Published manufacturer ranges span 3%–5% by volume. JetCat and KingTech currently specify 5% for kerosene engines; SWIWIN lists 3%–5%. Five percent (50 ml oil per liter) is the safe universal default; use 3% only if both your specific engine manual and your chosen oil support it.
They are the same fuel family but not identical products. Jet A-1 is aviation-specification kerosene (ASTM D1655) with tightly controlled freezing point, water and particulate limits. Store-bought 1-K kerosene (ASTM D3699) is accepted by the major engine manuals but varies more in cleanliness, so buy reputable fuel and filter it carefully.
No. 2 diesel is accepted conditionally by SWIWIN, JetCat and KingTech for ground testing and some flying, but it has lower lubricity (raise the oil percentage), produces more odor and smoke, and gels at roughly −10 to −15 °C. It is not recommended for cold-weather flight, and your engine manual should be checked before relying on it.
Gasoline's flash point is far below kerosene's, so its vapors can explode from a small spark or a hot engine during fueling — the dominant cause of serious turbine fuel accidents. It also vapor-locks fuel systems, causing unstable running or flameout. No manufacturer approves it, and using it voids the warranty.
Both are respected MIL-PRF-23699-class synthetic turbine oils, but approval lists differ by manufacturer — KingTech, for example, does not recommend AeroShell 500. Choose an oil by name from your engine manual's current approved list rather than by brand reputation alone, and never substitute two-stroke or automotive oil.
In sealed, dedicated, clearly labeled fuel cans, kept full, cool and out of sunlight to limit condensation; filter at every transfer, check for water or cloudiness before use, and don't keep mixed fuel for many months. Containers that previously held gasoline must never be reused.
No. The XX400WP uses a separate synthetic-oil lubrication system with its own tank, and runs on straight RP-3 aviation kerosene (equivalent to Jet A-1). Check the fuel and lubrication description for any engine larger than the RC class before mixing anything into its fuel.
The fuel specification for a model turbojet is genuinely simple once the logic is clear: clean kerosene — Jet A-1 wherever possible — mixed with a manufacturer-approved synthetic turbine oil, most conservatively at 5% by volume, filtered at every transfer and handled with standard hydrocarbon precautions. Diesel is a conditional option in mild weather, gasoline is never an option at all, and larger engines with independent oil systems run on straight aviation kerosene. Whatever engine you operate, the published manual for that exact engine remains the controlling document — and our team is glad to help you read it correctly.
Tell us the engine model and your operating climate. We'll confirm the approved fuel and oil specification, and quote the right engine — from SWIWIN model turbines to the XX400WP — for your UAV or industrial application.