Internal Combustion

Why This Matters

A steam engine is large, heavy, and takes 30-60 minutes to reach operating pressure. An internal combustion engine starts in seconds, fits on a workbench, and produces more power per kilogram than any steam engine ever could. It is the engine that powers vehicles, portable generators, chainsaws, water pumps, and tractors. Without access to gasoline or diesel fuel, you might assume these engines are useless — but they are not. Internal combustion engines can run on wood gas, ethanol distilled from fermented crops, or biodiesel made from animal fat and plant oil. This article teaches you how to make those fuels and adapt engines to burn them.

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Fuel Sources After Civilization

Petroleum refineries are gone. Gas station fuel degrades within 1-2 years (gasoline) or 5-10 years (diesel, with stabilizer). But internal combustion only needs a flammable gas or vapor mixed with air. Here are your four realistic options, ranked by ease:

1. Wood Gas (Producer Gas)

Easiest to produce. Lowest energy density.

When wood burns with limited air (partial combustion), it produces a mixture of carbon monoxide, hydrogen, and methane — collectively called “producer gas” or “wood gas.” This gas is flammable and can run any spark-ignition engine (gasoline engine). Millions of vehicles ran on wood gas during World War II when petroleum was rationed across Europe.

• Energy density: About 1/3 that of gasoline by volume. Expect 50-60% of the engine’s gasoline power rating
• Fuel consumption: Roughly 2-3 kg of dry wood per horsepower-hour
• Advantages: Fuel is everywhere. System can be built from scrap metal in days
• Disadvantages: Bulky gasifier, tar and ash management, engine power is reduced, carbon monoxide is lethal in enclosed spaces

2. Ethanol (Grain Alcohol)

Moderate difficulty. Good energy density.

Ethanol is the same alcohol in beer, wine, and spirits. At concentrations above 70% (140 proof), it burns in gasoline engines with minor adjustments. It is made by fermenting sugar or starch from crops, then distilling to remove water.

• Energy density: About 2/3 that of gasoline. Expect 70-80% of gasoline power with engine tuning
• Fuel consumption: About 1.5 liters of ethanol per liter of gasoline equivalent
• Advantages: Clean-burning, engine-friendly, liquid fuel (easy to store and transport)
• Disadvantages: Requires significant crop production, distillation equipment, and time. Competes with food supply
• Feedstocks: Corn, wheat, potatoes, sugar beets, fruit, honey, any starchy or sugary crop. Cellulose (wood, grass) is possible but requires acid hydrolysis first

3. Biodiesel

Moderate difficulty. Good energy density. Works in diesel engines only.

Biodiesel is made by chemically reacting vegetable oil or animal fat with methanol (or ethanol) and a catalyst (lye — sodium hydroxide). The result is a thin liquid fuel that runs in any diesel engine without modification.

• Energy density: Nearly equal to petroleum diesel
• Advantages: Diesel engines are more efficient than gasoline engines. Common in trucks, tractors, generators
• Disadvantages: Requires methanol (or ethanol) and lye. Animal fat supply is limited. Plant oil requires oil-seed crops (sunflower, rapeseed, soybean)
• Alternative: Straight vegetable oil (SVO) works in diesel engines if preheated to 70 degrees C to reduce viscosity. Requires a tank heater and a two-tank system (start on biodiesel/diesel, switch to hot SVO once warm)

4. Petroleum (If Found)

Hardest to produce. Highest energy density.

If your community discovers a natural oil seep, shallow petroleum deposit, or an intact storage tank, raw crude can be fractionally distilled into gasoline and diesel with relatively simple equipment — a heated vessel, a condenser coil, and collection vessels at different temperature ranges.

• Gasoline fraction: 35-200 degrees C
• Kerosene fraction: 150-275 degrees C
• Diesel fraction: 200-350 degrees C

This is beyond the scope of this article but worth knowing about. Early petroleum refining in the 1860s used equipment no more complex than a moonshine still.

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The Four-Stroke Cycle

Every gasoline and diesel engine you will encounter uses the four-stroke cycle. Understanding it is essential for troubleshooting and conversion.

Stroke 1 — Intake: The piston moves down, sucking in a fuel-air mixture through the open intake valve. Think of pulling back a syringe plunger.

Stroke 2 — Compression: Both valves close. The piston moves up, compressing the fuel-air mixture to 1/8 to 1/10 its original volume. Compression heats the gas significantly.

Stroke 3 — Power: In a gasoline engine, a spark plug fires, igniting the compressed mixture. The burning gas expands violently, driving the piston down. This is the only stroke that produces power. In a diesel engine, there is no spark plug — the compression alone heats the air to 500+ degrees C, and injected fuel ignites spontaneously.

Stroke 4 — Exhaust: The exhaust valve opens. The piston moves up, pushing burned gas out. Then the cycle repeats.

  INTAKE    →    COMPRESSION    →    POWER    →    EXHAUST
  (suck in)      (squeeze)          (bang!)        (push out)
  Piston down    Piston up          Piston down    Piston up
  Intake open    Both closed        Both closed    Exhaust open

The crankshaft makes two full revolutions (720 degrees) per cycle. The flywheel carries the engine through the three non-power strokes.

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What You Need

For a Wood Gasifier

• Steel container — a 200-liter (55-gallon) steel drum, a large fire extinguisher body, or a welded steel cylinder. This is the main reactor where wood is gasified
• Steel pipe — 5-10 cm (2-4 inch) diameter, several meters total, for gas routing and cooling
• Steel plate — for internal baffles, grate, and restriction plate
• Gasket material — high-temperature rope, ceramic fiber, or even wet clay for sealing joints
• Filter medium — wood chips, straw, or cloth for cleaning tar from the gas
• Coolant — a coiled pipe running through a bucket of water to cool the gas before it enters the engine
• Welding equipment — essential for gas-tight construction
• An engine — any gasoline/spark-ignition engine. Car engines, motorcycle engines, lawnmower engines, chainsaws, generators — all work

For Ethanol Distillation

• Fermentation vessel — food-grade plastic barrel, wooden barrel, or glass carboy. 50-200 liters
• Yeast — brewer’s yeast, bread yeast, or wild yeast from fruit skins. Turbo yeast gives highest alcohol yield
• Sugar or starch source — grain, potatoes, sugar beets, fruit, corn, honey
• Still — a pot (large cooking pot, pressure cooker, or steel drum), a condenser (coiled copper tubing running through cold water), and collection vessels
• Thermometer — essential for controlling distillation temperature. Ethanol boils at 78.4 degrees C; water boils at 100 degrees C
• Hydrometer — measures alcohol concentration. Scavenge from brewing supply stores or chemistry labs

For Biodiesel

• Vegetable oil or animal fat — 1 liter of oil yields about 1 liter of biodiesel
• Methanol — 200 ml per liter of oil. Scavenge from automotive windshield washer fluid (often 30-50% methanol) or distill from wood (wood alcohol = methanol, but this is toxic and requires careful handling)
• Sodium hydroxide (lye) — 3.5 grams per liter of oil for fresh oil; more for used cooking oil. Scavenge from drain cleaner (must be pure NaOH, no additives)
• Mixing container — glass or HDPE plastic. NOT aluminum (lye reacts violently with aluminum)
• Thermometer and scale

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Method 1: Building a Wood Gasifier

A gasifier converts solid wood into flammable gas through partial combustion in a restricted-air environment. The design below is a “downdraft” gasifier — the most practical type for engine fuel because it produces the least tar.

Step 1: Build the Reactor

1. Take a 200-liter steel drum. This is the outer shell and fuel hopper
2. Inside the drum, mount a smaller container (a 20-40 liter steel bucket, a cut-down fire extinguisher, or welded cylinder). This is the hearth zone where the actual gasification occurs
3. The hearth zone has:
   • Air inlet nozzles: 4-6 holes (10-15 mm diameter) evenly spaced around the circumference at mid-height. These are the only air entry points. Restricting air is what makes gas instead of just burning the wood
   • Restriction plate: A steel plate at the bottom of the hearth zone with a center hole (about 1/3 the hearth diameter). This forces all gas through the hottest zone, cracking tars into lighter gases
   • Grate: Below the restriction plate, a grate supports char and allows ash to fall through
4. The gas path: Wood feeds from the top hopper down through the hearth zone. Air enters through the nozzles. Gas exits downward through the restriction plate, through the char bed (which acts as a filter), and out through a pipe at the bottom of the drum

        WOOD IN (top)
            ↓
  ┌─────────────────────┐
  │    Fuel Hopper       │  ← 200L drum
  │    (drying zone)     │
  │─────────────────────│
  │    Hearth Zone       │  ← Inner container
  │  ●  Air Nozzles  ●  │  ← Restricted air in
  │─────────────────────│
  │    Restriction       │  ← Narrows gas path
  │─────────────────────│
  │    Char Bed          │  ← Filters tar
  │    Ash/Grate         │
  └──────────┬──────────┘
             │
         GAS OUT → filter → cooler → engine

Step 2: Build the Gas Cooling and Filtering System

Raw gas from the gasifier is hot (200-400 degrees C) and contains tar droplets, moisture, and fine ash. An engine cannot tolerate any of these.

1. Primary cooler: Run the gas pipe through a bucket of water or along a length of finned pipe in open air. The gas must cool to below 40 degrees C before entering the engine. Hot gas reduces engine power and can pre-ignite
2. Condensation trap: At the lowest point of the cooling pipe, install a drain valve. Water and heavy tars condense here. Drain this regularly — every 30-60 minutes during operation
3. Filter: Pass the gas through a container packed with clean wood chips, straw, or multiple layers of cloth. This catches fine particles and remaining tar. Replace or clean filter material frequently — every 4-8 hours of operation
4. Final filter: A container of dry sawdust as a final polishing filter before the engine intake

Step 3: Connect to the Engine

1. Mixing valve: The gas must be mixed with air before entering the engine. Build a simple mixing valve — a T-fitting where the gas pipe meets an air intake pipe, with a butterfly valve (a disk on a pivot inside the pipe) to adjust the gas-to-air ratio
2. Remove the carburetor from the engine (or leave it in place and feed gas through the air cleaner intake — simpler but less efficient)
3. Connect the gas pipe to the engine’s intake manifold or carburetor throat
4. Starting procedure:
   • Light the gasifier: open the top, place burning kindling in the hearth zone, close the top
   • Let the gasifier run for 5-10 minutes to build up gas production. The gas is initially too weak to burn
   • Test: hold a match to the gas outlet. When it lights with a steady blue or yellow flame, the gas is ready
   • Start the engine: crank it. It may take several attempts as gas fills the intake manifold
   • Adjust the mixing valve: too much gas (rich) = engine runs rough and smokes. Too much air (lean) = engine misfires and runs weak. Find the sweet spot
5. Engine timing: Wood gas burns slower than gasoline. If possible, advance the ignition timing by 10-15 degrees for better performance. On engines with a distributor, rotate the distributor body slightly against the direction of rotor rotation

Step 4: Operation and Maintenance

1. Fuel: Use dry, uniformly-sized wood chunks — 3-5 cm cubes or short sticks. Wet wood produces excessive tar and kills gas quality. Hardwood is better than softwood. Charcoal works best of all (nearly tar-free gas)
2. Refueling: Add wood through the top while running. Close the lid quickly — opening the hopper lets air in and disrupts gasification
3. Ash removal: Shake or vibrate the grate periodically to clear ash. Too much ash blocks airflow
4. Tar management: Tar is the biggest enemy. Signs of tar problems: engine runs poorly, dark sticky residue in pipes, filter clogs quickly. Solutions: run the gasifier hotter (more air through nozzles), use drier wood, use charcoal, clean filters more often

Warning

Wood gas contains 15-30% carbon monoxide, which is odorless and lethal. NEVER run a gasifier indoors or in an enclosed space. All connections must be gas-tight. If you feel dizzy, get to fresh air immediately. Carbon monoxide kills quickly and without warning.

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Method 2: Distilling Ethanol

Ethanol production is a two-step process: fermentation (sugar to alcohol using yeast) and distillation (separating alcohol from water by boiling point difference).

Step 1: Prepare the Mash

From grain (corn, wheat, barley, rye):

1. Grind or crush 25 kg of grain as fine as possible. A hand mill, mortar and pestle, or even a rock on a flat surface works
2. Mix with 75 liters of water in a large vessel (1:3 ratio by weight)
3. Heat to 65-68 degrees C and hold for 60-90 minutes, stirring frequently. This is mashing — enzymes in the grain convert starch to fermentable sugar. The temperature is critical: too low and conversion is slow, too high and enzymes are destroyed
4. For corn or potatoes (which lack sufficient enzymes), add malted barley — barley that has been soaked and sprouted for 3-5 days, then dried and ground. Use 2-3 kg of malt per 25 kg of corn/potato. The malt provides the enzymes
5. Cool the mash to below 35 degrees C before adding yeast. Hot liquid kills yeast

From sugar sources (fruit, honey, sugar beets):

1. Crush fruit or grate sugar beets and press out the juice
2. Dissolve honey in warm water (1:4 ratio)
3. No mashing needed — the sugar is already in fermentable form
4. Cool to below 35 degrees C

Step 2: Fermentation

1. Transfer the cooled mash to your fermentation vessel
2. Add yeast: 1 packet (7-11 grams) of bread yeast or brewer’s yeast per 20 liters. Sprinkle on top, stir gently
3. Seal the vessel with an airlock — a way for CO2 to escape without letting air in. The simplest airlock is a hose from the vessel lid into a jar of water. Bubbles in the water show active fermentation
4. Keep at 20-30 degrees C. Too cold = slow fermentation. Too hot = yeast dies or produces off flavors
5. Fermentation takes 5-14 days. It is done when bubbling stops
6. The resulting liquid (“wash” or “beer”) is 8-15% alcohol depending on sugar content and yeast strain

Step 3: Distillation

You need to concentrate the 8-15% alcohol to at least 70% (140 proof) for engine fuel. This requires distillation — heating the wash to evaporate alcohol (boils at 78.4 degrees C) while leaving most of the water behind (boils at 100 degrees C).

1. The pot: A large sealed vessel — a pressure cooker is ideal because it already has a sealed lid with a steam outlet. A modified steel drum works too. Fill 2/3 with fermented wash
2. The column (optional but improves purity): A vertical pipe packed with copper scrubbers, glass marbles, or steel wool, mounted on top of the pot. Vapor rises through the packing, and heavier water vapor condenses and drips back while lighter alcohol vapor continues upward. A column 60-90 cm tall packed with copper mesh can produce 80-90% alcohol in a single pass
3. The condenser: A coiled copper tube (3-5 meters of 10-15 mm tubing) running through a bucket of cold water. Alcohol vapor enters the top of the coil, condenses back to liquid as it cools, and drips out the bottom into your collection vessel
4. Heat control is critical: Apply heat slowly. Monitor the thermometer at the top of the column or at the condenser inlet:
   • Below 78 degrees C: Mostly methanol (“foreshots”). Collect and DISCARD the first 50-100 ml per 20 liters of wash. Methanol is poisonous — it causes blindness and death. This is not optional
   • 78-82 degrees C: This is your target range. Mostly ethanol. Collect this into your fuel container
   • Above 85 degrees C: Increasing water content. The alcohol concentration is dropping. Stop collecting when the temperature stabilizes above 90 degrees C
5. Second distillation (recommended for fuel): Run your first collection through the still a second time. This concentrates the ethanol further, often reaching 85-92%
6. Testing concentration: Float a hydrometer in the output. For engine fuel, you need at least 150 proof (75%). Higher is better — 180 proof (90%) runs cleanest

Step 4: Engine Conversion for Ethanol

Most gasoline engines run on ethanol with minor modifications:

1. Fuel system: Ethanol is more corrosive to rubber than gasoline. Replace rubber fuel lines with ethanol-resistant hose (nylon, stainless steel braided, or modern fuel-injection hose). Old natural-rubber gaskets in the carburetor may swell — replace with synthetic
2. Jet size: Ethanol requires about 40% more fuel volume than gasoline for the same power (lower energy density). Enlarge the carburetor main jet by 30-40%. Drill it out carefully with the next larger drill size
3. Ignition timing: Ethanol has a higher octane rating than gasoline (about 113 vs. 87-93). This means you can advance the ignition timing by 5-10 degrees for better efficiency and power without knocking
4. Cold starting: Ethanol is harder to start in cold weather. Keep a small supply of gasoline (if available) or start with a propane torch held near the intake for initial ignition
5. Compression ratio: If you are rebuilding an engine, a higher compression ratio (12:1 instead of the stock 8-10:1) extracts more power from ethanol. You can raise compression by milling the cylinder head (removing material from the mating surface). This is advanced work

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Method 3: Making Biodiesel

Biodiesel works in any diesel engine without modification. The process is a chemical reaction called transesterification.

Step 1: Prepare the Oil

1. Collect vegetable oil (sunflower, rapeseed, soybean, peanut) or render animal fat (tallow, lard). Filter through cloth to remove food particles
2. Test for free fatty acid (FFA) content (used oil only): Dissolve 1 ml of oil in 10 ml of isopropyl alcohol (rubbing alcohol). Add drops of lye solution (1 gram NaOH in 1 liter water) while stirring until the mixture turns and stays pink (add a drop of phenolphthalein indicator if available, or use turmeric — it turns red/brown with base). Count the ml of lye solution used. Fresh oil needs about 3.5 grams of NaOH per liter; used oil needs more — add 1 gram extra per ml of lye solution used in the test
3. Heat the oil to 55 degrees C (not above 60 degrees C)

Step 2: Mix the Methoxide

Safety Warning

Methanol is toxic — absorbed through skin and lungs. Causes blindness and death. Sodium hydroxide (lye) causes severe chemical burns. Wear gloves, eye protection, and work outdoors. Never inhale methanol vapors.

1. Measure 200 ml of methanol per liter of oil
2. Measure the calculated amount of NaOH (3.5 grams per liter for fresh oil, more for used)
3. Add the NaOH to the methanol in a sealed glass or HDPE container. Shake until fully dissolved (5-10 minutes). The mixture will heat up — this is normal. The result is sodium methoxide
4. This must be used within 2 hours — it degrades on standing

Step 3: React

1. Pour the sodium methoxide into the warm oil (55 degrees C)
2. Stir vigorously for 30-60 minutes. A hand drill with a paint stirring attachment works well. The mixture will become cloudy then gradually clear
3. Pour into a tall, clear container (a clear plastic bottle works)
4. Let stand for 8-24 hours. Two layers will separate:
   • Top layer (light amber): Biodiesel — your fuel
   • Bottom layer (dark, syrupy): Glycerin — a byproduct (useful as soap base, lubricant, or skin moisturizer)
5. Drain off the glycerin from the bottom

Step 4: Wash and Dry

1. Add warm water (about 1/3 the volume of biodiesel) and gently agitate. The water absorbs residual methanol, lye, and soap
2. Let separate for 2-4 hours. Drain the water from the bottom
3. Repeat 2-3 times until wash water is clear
4. Dry the biodiesel: let it sit uncovered in a warm place for 24-48 hours, or bubble air through it using an aquarium pump. Water in biodiesel causes injector problems
5. The finished fuel should be clear amber. Cloudy fuel still contains water — keep drying

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Common Mistakes

Mistake	Why It’s Dangerous	What to Do Instead
Running a gasifier indoors	Carbon monoxide accumulation kills without warning	Always operate gasifiers outdoors with good ventilation
Using wet wood in the gasifier	Excessive tar clogs filters and engine; gas quality too low to run	Dry wood for weeks. Under 20% moisture content is essential
Skipping the foreshots during distillation	Methanol in the first runnings causes blindness and death	Always discard the first 50-100 ml per 20 liters of wash
Using aluminum containers with lye (biodiesel)	Violent exothermic reaction; container can melt or explode	Use glass, HDPE plastic, or stainless steel only
Not filtering gasifier gas before engine	Tar and ash destroy piston rings, clog valves, score cylinder walls	Always use cooling, condensation trap, and at least two filter stages
Fermenting above 35 degrees C	Yeast dies; fermentation fails; wasted feedstock	Keep fermentation between 20-30 degrees C
Running ethanol in unmodified fuel lines	Ethanol dissolves rubber; fuel lines crack and leak	Replace rubber lines with nylon or braided stainless
Heating oil above 60 degrees C for biodiesel	Methanol boils off; reaction fails; fire risk	Use a thermometer. Hold at 55 degrees C
Not testing biodiesel FFA level	Wrong lye amount means incomplete reaction; fuel turns to soap	Always titrate used oil before processing
Ignoring engine timing adjustments	Wood gas and ethanol burn differently than gasoline; power loss and damage	Advance timing 10-15 degrees for wood gas, 5-10 degrees for ethanol

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What’s Next

With internal combustion capability, your community can power:

• Vehicles and transport — convert trucks, motorcycles, and tractors to run on wood gas or ethanol
• Portable generators — ethanol-powered generators provide electricity anywhere, not just near rivers or on windy hilltops
• Agricultural equipment — tractor-powered plowing, harvesting, and transport transform food production capacity
• Combine with: Steam Engine — use steam for fixed installations (sawmills, workshops), internal combustion for mobile and portable applications
• Combine with: Telecommunications — reliable engine-driven generators power telephone exchanges and radio transmitters 24/7

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Quick Reference Card

Internal Combustion — At a Glance

Three fuel paths:

Fuel	Source	Difficulty	Engine Type
Wood gas	Dry wood/charcoal in gasifier	Moderate	Gasoline (spark)
Ethanol	Fermented grain/sugar, distilled	Moderate-Hard	Gasoline (spark)
Biodiesel	Oil/fat + methanol + lye	Moderate	Diesel

Wood Gasifier Quick Build:

1. 200L drum with inner hearth zone, 4-6 air nozzles, restriction plate
2. Gas cooling pipe through water bucket
3. Condensation drain, wood chip filter, sawdust polishing filter
4. Mixing valve (gas + air) to engine intake
5. Light gasifier, wait 5-10 min, test flame, start engine

Ethanol Distillation:

1. Ferment grain/sugar mash with yeast (5-14 days, 20-30 degrees C)
2. Distill: DISCARD first 50-100 ml (methanol — poison)
3. Collect at 78-82 degrees C until temp exceeds 85 degrees C
4. Second run for higher concentration (target: 75%+)

Biodiesel:

1. Heat oil to 55 degrees C
2. Mix methanol (200 ml/L oil) + NaOH (3.5 g/L fresh oil) = sodium methoxide
3. Stir into warm oil for 30-60 min
4. Settle 8-24 hours, drain glycerin, wash 3x with warm water, dry

Critical safety rules:

• NEVER run a gasifier indoors (carbon monoxide kills)
• ALWAYS discard foreshots when distilling (methanol is lethal)
• NEVER use aluminum with lye
• Advance engine timing for alternative fuels

Remember: Dry fuel in, clean gas out. Every filter stage you skip costs engine life.