What are the sources of internal combustion?

Internal combustion is powered primarily by fuels such as gasoline, diesel, natural gas, LPG, biofuels (ethanol, biodiesel, renewable diesel), synthetic e-fuels, and increasingly hydrogen—with ambient air (oxygen) and an ignition source completing the reaction. In practical terms, “sources” refers to the energy carriers and enabling inputs that allow an engine to burn fuel inside the cylinder to produce mechanical work.

What “sources” means in engine context

In an internal combustion engine (ICE), energy release occurs when a fuel reacts with an oxidizer—almost always oxygen in air—inside the combustion chamber. Source, therefore, encompasses three elements: the fuel itself (the chemical energy), the oxidizer (usually air), and the ignition method (spark, compression heat, or other). The mix of these determines engine design, performance, emissions, and safety.

Primary fuel families used in internal combustion engines today

The following list groups the main fuel sources that currently power internal combustion across road, off‑road, marine, aviation, and stationary applications.

• Petroleum-derived liquids (gasoline/petrol, diesel, kerosene/jet fuel, heavy fuel oil)
• Gaseous hydrocarbons (natural gas as CNG/LNG, LPG/propane–butane, syngas in stationary engines)
• Bio-based fuels (bioethanol, biodiesel/FAME, renewable diesel/HVO, biomethane/biogas, biomethanol, bio‑DME)
• Synthetic and e-fuels (Fischer–Tropsch drop-in diesel/kerosene/gasoline, e-methane, e-methanol, e‑kerosene)
• Hydrogen and emerging carriers (gaseous hydrogen for ICEs, hydrogen blends, ammonia under active development)

Together, these categories capture today’s commercial fuels and the leading low‑carbon contenders engineered to work in existing or adapted engines.

Petroleum-derived liquids

This group remains the dominant energy source for road transport and aviation, valued for energy density, global supply chains, and engine compatibility.

• Gasoline (petrol): Used in spark‑ignition engines; typically blended with 5–10% ethanol (E5–E10) in many markets.
• Diesel: For compression‑ignition engines across trucks, buses, rail, and off‑road; ultra‑low sulfur grades are standard in most advanced markets.
• Kerosene/Jet fuel (Jet A/A-1): Aviation turbines and some heaters; also used as a diesel substitute in extreme cold.
• Heavy fuel oil (HFO)/marine bunker: Two‑stroke marine engines; increasingly supplemented by low‑sulfur fuel oils and LNG to meet IMO emissions rules.
• Naphtha and specialty blends: Feedstock or alternative gasoline-range fuel in certain industrial and fleet contexts.

While mature and ubiquitous, these fuels face tightening emissions and climate constraints, driving interest in low‑carbon drop‑ins and alternatives.

Gaseous hydrocarbons

Gaseous fuels offer cleaner combustion than many liquids, with growing roles in heavy‑duty transport and stationary power.

• Natural gas: Used as CNG (compressed) or LNG (liquefied); popular in buses, long‑haul trucks, ferries, and peaker plants.
• LPG (propane–butane): Common in light‑duty fleets, rural heating, forklifts; lower particulates than gasoline/diesel.
• Associated/flare gas and field gas: Captured and conditioned for stationary engines to reduce flaring.
• Syngas (CO + H2): Produced from gasified biomass/waste; used in some CHP and industrial engines.

Adoption depends on fueling infrastructure and engine calibration, but lifecycle emissions can be favorable—especially when paired with biomethane.

Bio-based fuels

Biogenic fuels can reduce lifecycle greenhouse gases and are often compatible with existing engines, making them key transition options.

• Bioethanol: Fermented from corn/sugarcane/cellulosics; blended as E10 globally and up to E85 in flex‑fuel vehicles.
• Biodiesel (FAME): Fatty-acid methyl esters from oils and fats; used in blends like B5–B20 and as B100 in approved engines.
• Renewable diesel (HVO): Hydrotreated vegetable oil/waste fats; a drop‑in diesel substitute (HVO100) with strong cold‑flow and emissions performance.
• Biogas/biomethane: Upgraded to pipeline‑quality RNG for CNG/LNG vehicles and stationary engines.
• Biomethanol and bio‑DME: Emerging options for compression ignition with soot reductions and potential in marine/off‑road.

Feedstock sustainability and supply scale are pivotal; advanced pathways (waste, residues, cellulosics) are expanding to address indirect land-use concerns.

Synthetic and e-fuels

These fuels are manufactured from hydrogen and carbon sources and can be drop‑in compatible, targeting hard‑to‑electrify segments.

• Fischer–Tropsch (FT) fuels: Synthetic diesel, kerosene, and gasoline from biomass, waste, or captured CO2 plus green hydrogen.
• E‑methane (synthetic natural gas): Methanation of CO2 with green H2; usable in existing CNG/LNG engines and grids.
• E‑methanol and e‑kerosene: Growing interest in marine and aviation; pilot production scaling in the 2020s.

With renewable electricity as the upstream energy, e‑fuels can be near‑carbon‑neutral, though costs and power requirements remain significant.

Hydrogen and emerging carriers

Hydrogen can be burned in modified ICEs, offering zero CO2 at the tailpipe, though NOx control and storage challenges remain; ammonia is being trialed as a hydrogen carrier fuel for engines.

• Hydrogen (gaseous): Deployed in prototype and early commercial ICEs for trucks/off‑road; manufacturers have announced development programs and pilot fleets.
• Hydrogen blends and dual‑fuel: Hydrogen co‑firing with natural gas or pilot diesel to reduce carbon intensity.
• Ammonia (NH3): Under marine and stationary engine development as a carbon‑free fuel; typically requires pilot fuel and advanced aftertreatment.

These pathways are advancing quickly in heavy‑duty and marine sectors, with 2024–2025 marking the first commercial ammonia-capable marine engines and broader hydrogen ICE pilots.

Oxidizer and ignition sources that enable combustion

Besides fuel, combustion needs oxygen and a means to initiate the reaction. The items below summarize how engines supply oxidizer and trigger ignition across technologies.

• Oxidizer: Ambient air is standard; oxygen‑enriched air and nitrous oxide are specialty cases. Exhaust gas recirculation (EGR) deliberately dilutes oxygen to control NOx and combustion temperature.
• Intake conditioning: Turbo/supercharging increases oxygen per cycle; intercooling improves charge density and knock resistance.

Tuning the intake oxygen content and temperature is central to balancing power, efficiency, and emissions.

The ignition methods below are the primary “spark” that transforms the fuel–air mix into a controlled burn.

• Spark ignition (SI): Spark plug ignites premixed charge (gasoline, many gaseous fuels, some alcohols).
• Compression ignition (CI): Fuel auto‑ignites under high pressure/temperature (diesel, HVO, some synthetic and bio‑fuels).
• Pilot ignition and pre‑chambers: Small injections or pre‑chambers stabilize combustion in lean or difficult fuels (natural gas, hydrogen, ammonia R&D).
• Auxiliary aids: Glow plugs, hot-surface ignition, and experimental laser ignition.

Choice of ignition governs engine architecture and fuel compatibility, influencing efficiency, noise, and aftertreatment needs.

Common blends and compatibility notes

Many markets rely on blended fuels to balance performance, emissions, and supply. The following examples illustrate typical practice and constraints.

• Gasoline blends: E10 is widespread; E85 for flex‑fuel vehicles. Octane rating and ethanol content affect compatibility.
• Diesel blends: B5–B20 common; B100 and HVO100 approved for certain engines. Cold‑flow additives and material compatibility matter.
• Gaseous fuels: CNG/LNG and LPG require dedicated fueling hardware and engine calibration; biomethane is a drop‑in for CNG/LNG systems.

Always consult engine certifications and local standards (e.g., ASTM/EN) before switching fuels or blend levels to avoid warranty and emissions compliance issues.

Safety, emissions, and policy context

Fuel choice shapes both operational hazards and environmental footprint. The points below highlight practical considerations.

• Safety: Hydrogen and LPG demand rigorous leak detection and ventilation; LNG requires cryogenic handling; ammonia is toxic and corrosive.
• Emissions: Tailpipe pollutants (NOx, PM, CO) vary by fuel and ignition strategy; aftertreatment (DOC/DPF/SCR/three‑way catalysts) is often essential.
• Climate: Lifecycle CO2 depends on feedstock and process—biogenic and e‑fuels can be low‑carbon if produced with sustainable inputs and renewable electricity.
• Policy trends: Many jurisdictions tighten engine emissions and encourage low‑carbon fuels; the EU has carved out a pathway for e‑fuel ICEs post‑2035, while heavy‑duty sectors expand RNG, HVO, and LNG use.

As standards evolve, internal combustion is increasingly paired with cleaner fuels and advanced controls to meet air‑quality and climate goals.

Summary

Internal combustion relies on three sources: a combustible fuel, oxygen from air, and an ignition mechanism. Today’s fuels range from petroleum liquids and gaseous hydrocarbons to biofuels, synthetic e‑fuels, hydrogen, and emerging ammonia. How engines admit oxygen and initiate ignition—spark, compression, or pilot—determines compatibility and emissions. With policy and technology accelerating, drop‑in low‑carbon liquids (HVO, FT fuels), renewable gases (biomethane), and hydrogen/ammonia pilots are expanding the fuel toolbox while leveraging existing ICE platforms.

What are the three things for internal combustion?

An internal combustion engine needs fuel, air, and a spark to operate effectively. Fuel provides energy, air supplies oxygen for combustion, and the spark ignites the mixture.

How does internal combustion occur?

In a spark ignition engine, the fuel is mixed with air and then inducted into the cylinder during the intake process. After the piston compresses the fuel-air mixture, the spark ignites it, causing combustion.

What are the 5 key events common to all internal combustion engines?

A four-stroke cycle engine completes five Strokes in one operating cycle, including intake, compression, ignition, power, and exhaust Strokes. The intake event is when the air-fuel mixture is introduced to fill the combustion chamber.

What are the main sources of combustion?

Examples of these combustion sources include steam/electric generating plants, industrial boilers, steel mills, and commercial and domestic combustion units. Coal, fuel oil, and natural gas are the major fossil fuels used by these sources.