Engine Pistons Explained: Types, Metallurgy, Manufacturing and Performance Applications

The piston is one of the most highly stressed components inside an internal-combustion engine.engine piston types

During operation it must transfer combustion pressure into mechanical force while simultaneously surviving extreme temperature gradients, rapid acceleration reversals, side loading against the cylinder wall, ring friction, cyclic fatigue and—in performance engines—occasional abnormal combustion events.

Choosing a piston therefore involves considerably more engineering than simply deciding whether an engine needs a "forged piston."

The piston material, alloy composition, manufacturing method, crown geometry, ring-land design, pin location, skirt profile, thermal expansion and cooling strategy must all be matched to the engine's intended cylinder pressure, RPM range, operating temperature and duty cycle.

Modern piston engineering covers everything from low-expansion cast aluminium pistons designed for quiet road-car operation to highly ductile forged racing pistons and extremely strong steel pistons used in highly loaded diesel engines.

What Does an Engine Piston Actually Have to Survive?

During combustion, gas pressure acts on the piston crown and generates the force transmitted through the gudgeon—or wrist—pin and connecting rod to the crankshaft.

However, combustion pressure represents only one part of the piston loading.

A piston must withstand:

• combustion pressure acting on the crown;

• thermal loading from combustion gases;

• cyclic thermal expansion and contraction;

• tensile and compressive inertial loads at high RPM;

• lateral thrust against the cylinder bore;

• friction from the piston rings and skirt;

• loading around the piston-pin bosses;

• ring-land loading;

• fatigue caused by millions of combustion cycles;

• oil-film disruption;

• pre-ignition or detonation events;

• localised temperature concentrations around the crown and ring belt.

This is why a piston designed for a quiet production engine may be completely inappropriate for a competition engine producing several times the original specific output.

Main Types of Engine Pistons

Pistons can be classified in several ways, but from an engineering perspective the most important distinction is generally their material and manufacturing process.

Cast Aluminium Pistons

Cast pistons are manufactured by introducing molten aluminium alloy into a mould where it solidifies into a near-net piston blank.

Casting allows complex shapes to be produced economically and is therefore extremely common in mass-production engines.

Modern cast pistons should not be dismissed as "weak." Properly engineered aluminium-silicon casting alloys can support significant combustion pressures, particularly when combined with controlled microstructures, cooling galleries, reinforced ring grooves and optimised crown geometry.

MAHLE, for example, produces commercial-vehicle aluminium pistons from high-temperature-resistant aluminium-silicon alloys for engines operating at peak cylinder pressures exceeding 200 bar.

The primary advantages of cast pistons include:

• comparatively low manufacturing cost;

• good dimensional stability;

• relatively low thermal expansion when high-silicon alloys are used;

• low cold-start noise;

• tight piston-to-wall clearances;

• good wear resistance;

• excellent suitability for large-volume OEM manufacturing.

The trade-off is normally lower ductility and reduced tolerance of severe overload compared with suitable high-strength forged alloys.

Forged Aluminium Pistons

A forged piston begins as a solid aluminium alloy billet or preform which is plastically deformed under high pressure into a piston blank.

Forging changes the material structure compared with conventional casting. MAHLE notes that, for the same alloy, forged pistons exhibit a finer microstructure and greater strength than cast pistons, allowing their use in highly loaded series-production and motorsport engines.

Forging can also permit reduced wall thickness in appropriate areas, helping engineers control piston mass.

Forged pistons are therefore common in:

• high-output turbocharged engines;

• motorsport engines;

• highly tuned naturally aspirated engines;

• engines exposed to sustained high cylinder pressure;

• competition engines with high thermal loading;

• applications where occasional abnormal combustion must be tolerated.

However, the word forged does not define the piston alloy.

A forged 4032 piston and a forged 2618 piston behave significantly differently despite both being manufactured by forging.

That distinction is extremely important.

Piston Metallurgy: Why the Aluminium Alloy Matters

Aluminium dominates passenger-car and performance piston construction because it provides a very favourable combination of low density, thermal conductivity, machinability and mechanical properties.

But aluminium itself is too soft for demanding piston service.

Engineering properties are created by alloying aluminium with elements including silicon, copper, magnesium, nickel, iron and others.

For high-performance aftermarket pistons, two alloy families are particularly important:

4032 aluminium and 2618 aluminium.

4032 Aluminium Pistons

4032 is a high-silicon wrought aluminium alloy widely used for forged pistons.

According to EN 573-3 composition data, 4032 contains approximately:

• 11.0–13.5% silicon;

• 0.50–1.30% copper;

• 0.80–1.30% magnesium;

• 0.50–1.30% nickel;

• aluminium forming the balance.

The high silicon concentration contributes substantially to its piston behaviour.

Silicon reduces the coefficient of thermal expansion of aluminium and improves wear characteristics.

This means a 4032 piston can normally operate with a smaller piston-to-cylinder clearance than an equivalent low-silicon 2618 piston.

The practical advantages can include:

• quieter cold operation;

• reduced piston slap;

• improved dimensional stability;

• tighter cold piston-to-wall clearance;

• good wear characteristics;

• reduced cold-engine oil consumption potential.

MAHLE specifically uses 4032 in performance applications where tighter cylinder-wall clearances and improved temperature stability are desired.

Is 4032 Really a Hypereutectic Alloy?

This term deserves clarification.

The aluminium-silicon eutectic composition is around the region of 12–13% silicon depending on the precise thermodynamic conditions and additional alloying elements.

4032 contains approximately 11–13.5% silicon.

Consequently, describing every 4032 piston simply as "hypereutectic" is not metallurgically precise because the permitted composition range extends around the eutectic region.

In aftermarket terminology, 4032 is sometimes grouped with high-silicon or hypereutectic piston materials because of its high silicon content and low expansion behaviour.

A more technically accurate description is:

4032 is a high-silicon aluminium forging alloy whose silicon concentration lies around the Al-Si eutectic composition.

By comparison, dedicated hypereutectic casting alloys deliberately contain silicon above the eutectic concentration.

2618 Aluminium Pistons

2618 is a substantially different alloy.

It is a copper-magnesium-nickel aluminium alloy with very little silicon.

Typical 2618A composition includes approximately:

• 1.8–2.7% copper;

• 1.2–1.8% magnesium;

• 0.8–1.4% nickel;

• 0.9–1.4% iron;

• maximum silicon around 0.25%;

• aluminium as the balance.

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The exact chemistry depends on the applicable 2618/2618A specification.

2618 was originally associated with demanding aerospace applications and has become particularly important in motorsport because of its strength, elevated-temperature capability and toughness.

Compared with 4032, 2618 generally provides greater ductility and greater tolerance of extreme mechanical and abnormal-combustion loading.

MAHLE consequently describes 2618 as the choice offering increased resistance to detonation-related loading in its performance piston range.

This requires an important distinction:

A 2618 piston does not prevent detonation.

Its mechanical properties can simply make the piston more tolerant of the enormous transient loading generated when detonation occurs.

Engine calibration, combustion-chamber design, fuel quality, charge temperature, ignition timing and boost remain responsible for controlling abnormal combustion.

The Disadvantage of 2618: Thermal Expansion

Low silicon content means that 2618 expands considerably more as temperature increases.

Consequently, the piston must generally be installed with more cold piston-to-wall clearance than a comparable 4032 design.

Potential consequences include:

• more cold piston noise;

• increased piston slap before operating temperature is reached;

• potentially greater cold oil consumption;

• greater dependence on correct bore clearance;

• greater sensitivity to unsuitable warm-up behaviour.

This does not make 2618 inferior.

It simply makes it optimised for a different engineering objective.

For a highly boosted competition engine, accepting additional cold clearance may be entirely reasonable in exchange for increased toughness and overload tolerance.

For a road engine expected to start quietly every morning and cover 150,000 km, the priorities may be very different.

2618 vs 4032 Forged Pistons

4032

Best suited where priorities include:

• road use;

• low cold-start noise;

• tighter piston-to-wall clearance;

• good wear behaviour;

• moderate-to-high performance;

• long-duration street operation.

2618

Best suited where priorities include:

• very high cylinder pressure;

• aggressive turbocharging;

• competition use;

• high specific output;

• severe thermal loading;

• increased tolerance to transient overload;

• racing duty cycles.

There is no universally "better" alloy.

The correct material is the one appropriate for the operating conditions.

Cast Hypereutectic Aluminium Pistons

Hypereutectic piston alloys contain more silicon than the aluminium-silicon eutectic composition.

During solidification, primary silicon particles form within the aluminium matrix.

When the alloy, casting process and subsequent machining are correctly controlled, this can provide excellent:

• dimensional stability;

• wear resistance;

• scuff resistance;

• thermal-expansion behaviour.

Modern hypereutectic casting technology can therefore produce extremely capable production pistons.

SAE research into high-performance cast aluminium diesel pistons has demonstrated how controlling alloy chemistry, casting conditions and local microstructure can significantly improve fatigue behaviour in highly thermally loaded combustion-bowl regions.

This again illustrates why the simplistic claim that "forged is always better than cast" is technically incorrect.

The required component properties depend on the engine application.

Steel Pistons

Although aluminium remains dominant in petrol engines, steel piston technology has become increasingly important in highly loaded diesel applications.

Steel possesses substantially greater mechanical strength and a lower coefficient of thermal expansion than aluminium.

MAHLE publishes representative values illustrating the fundamental difference:

• aluminium density: approximately 2.7 g/cm³;

• steel density: approximately 7.8 g/cm³;

• aluminium thermal expansion: approximately 21 × 10⁻⁶/K;

• steel thermal expansion: approximately 12 × 10⁻⁶/K.

Steel therefore expands significantly less but is considerably denser.

The high material strength allows engineers to reduce wall thickness and compression height sufficiently that modern steel piston concepts can offset some of the material's density disadvantage.

Steel pistons are especially attractive when peak cylinder pressure and combustion temperature push aluminium towards its mechanical limits.

MAHLE and Kolbenschmidt both employ steel piston technology in heavy-duty and modern diesel applications.

Composite and Articulated Pistons

Not every piston is manufactured from a single material.

Large diesel and industrial engines may use composite piston construction.

Examples include:

• forged steel crown with aluminium skirt;

• forged steel crown with nodular cast-iron skirt;

• all-steel composite constructions;

• friction-welded steel pistons;

• brazed steel pistons.

The crown can therefore provide the mechanical and thermal resistance required around the combustion chamber while the skirt material is optimised for mass, friction and cylinder interaction.

MAHLE uses several such constructions in large-engine applications.

How Pistons Are Manufactured

Aluminium Piston Casting

A typical cast-piston manufacturing sequence includes:

1. aluminium alloy preparation;

2. melting and chemistry control;

3. mould filling;

4. controlled solidification;

5. heat treatment where required;

6. rough machining;

7. CNC machining of crown, skirt, pin bore and ring grooves;

8. surface treatment or coating;

9. dimensional inspection;

10. weight classification and quality control.

Controlling cooling rate and microstructure is critical.

Porosity, silicon morphology, intermetallic phases and grain structure can all influence piston fatigue performance.

Forged Piston Manufacturing

Forged pistons begin with wrought alloy stock.

The material is heated to the appropriate forging temperature and plastically formed under substantial pressure.

The forged blank is subsequently heat treated and extensively machined.

A simplified production route is:

1. alloy billet or slug production;

2. billet heating;

3. forging/preforming;

4. final die forging;

5. heat treatment;

6. CNC crown machining;

7. ring-groove machining;

8. pin-bore machining;

9. skirt profiling;

10. final finishing;

11. coating and surface treatment;

12. inspection.

Because much of the final geometry is CNC-machined, forged performance pistons can incorporate extremely specific crown and skirt configurations.

Piston Crown Geometry

The crown is not merely the top surface of the piston.

It forms part of the combustion chamber and can have a significant influence on:

• compression ratio;

• combustion-chamber volume;

• flame propagation;

• mixture motion;

• valve clearance;

• knock behaviour;

• direct-injection spray interaction;

• squish or quench;

• thermal loading.

Flat-Top Pistons

A flat-top piston provides a relatively simple crown profile and can offer a favourable surface-area-to-volume relationship.

However, even a so-called flat-top piston may contain valve pockets and subtle crown machining.

Dished Pistons

A dish increases clearance volume and can therefore reduce compression ratio.

Dished crowns are frequently used in turbocharged petrol engines where combustion chamber volume, compression ratio and piston crown thickness must be balanced.

Domed Pistons

A dome reduces combustion-chamber clearance volume and generally increases compression ratio.

Domes have historically been used in high-compression naturally aspirated engines.

An excessively large dome, however, can obstruct flame travel and negatively affect combustion.

Compression ratio should therefore never be considered independently of combustion-chamber geometry.

Diesel Bowl Pistons

Direct-injection diesel pistons typically incorporate a carefully engineered combustion bowl.

Its geometry influences:

• fuel spray interaction;

• swirl;

• mixture formation;

• soot formation;

• combustion speed;

• thermal concentration around the bowl rim.

The bowl rim is also one of the areas subjected to severe thermal fatigue, which is why diesel piston metallurgy and internal cooling are particularly important.

Full-Skirt and Slipper-Skirt Pistons

Traditional pistons can employ relatively extensive skirt area around the piston circumference.

High-performance pistons frequently use slipper-skirt configurations where material is removed from low-load regions.

The objectives include:

• lower reciprocating mass;

• reduced skirt contact area;

• reduced friction;

• improved access around crankshaft counterweights.

MAHLE uses lightweight slipper-skirt forgings extensively in its motorsport piston range.

Reducing material is not automatically beneficial, however.

The remaining piston structure must still maintain sufficient stiffness around the pin bosses, skirt and crown.

Ring Lands and Ring Grooves

The area between the piston crown and skirt forms the ring belt.

The sections separating the ring grooves are called ring lands.

These areas experience severe thermal and mechanical loading.

Excessive cylinder pressure or detonation can fracture a ring land even when the remainder of the piston appears undamaged.

Ring groove geometry must also remain extremely precise.

Excessive groove distortion can compromise ring sealing and increase blow-by or oil consumption.

Diesel pistons may incorporate cast-in iron or steel ring carriers to increase groove durability.

MAHLE uses high-nickel iron groove inserts in certain heavy-duty aluminium pistons specifically to reduce ring-groove wear.

Piston Pin Bosses

The piston pin transmits combustion and inertial forces between the piston and connecting rod.

The surrounding pin-boss structure therefore experiences very high cyclic loading.

Performance piston design must balance:

• pin diameter;

• pin wall thickness;

• pin length;

• boss stiffness;

• piston mass;

• pin offset;

• crown support.

Reducing piston-pin mass can help high-RPM operation, but excessive reduction in pin stiffness can cause pin deflection and localise loading in the piston bosses.

Everything is a compromise.

Thermal Expansion and Piston-to-Wall Clearance

A piston cannot simply be manufactured at exactly the same diameter as the cylinder bore.

The piston expands dramatically as operating temperature rises.

It therefore requires a calculated cold clearance.

The correct clearance depends on factors including:

• piston alloy;

• piston diameter;

• skirt design;

• bore material;

• cylinder coating;

• expected piston temperature;

• power level;

• cooling system;

• intended duty cycle;

• manufacturer-specific skirt profile.

This is particularly important when comparing 2618 and 4032 pistons.

A 2618 piston generally needs greater cold clearance because of its greater thermal expansion.

A 4032 piston can normally run tighter.

Generic piston-to-wall clearance figures should never replace the piston manufacturer's specification.

The manufacturer has already accounted for the alloy and the intentional barrel-shaped and oval skirt geometry.

Why Pistons Are Not Perfectly Round

A cold piston may appear approximately cylindrical, but precision piston skirts are intentionally manufactured with complex geometry.

They can incorporate both:

Ovality:Different diameters across the piston-pin axis and thrust axis.

Barrel profile:A changing skirt diameter from top to bottom.

This compensates for:

• non-uniform temperature distribution;

• different structural stiffness around the pin bosses;

• controlled skirt contact;

• thermal distortion during operation.

A correctly designed piston approaches its intended operating geometry only once thermal and mechanical loading are present.

Piston Temperature and Heat Transfer

A major proportion of piston thermal management occurs through:

• piston rings into the cylinder wall;

• skirt and oil film;

• piston pin;

• oil jets beneath the crown;

• internal cooling galleries in some piston designs.

Aluminium has considerably higher thermal conductivity than steel, allowing combustion heat to move through the component comparatively quickly.

Steel conducts heat less rapidly, which produces a different piston temperature distribution.

SAE research comparing geometrically similar aluminium and steel diesel pistons found measurable differences in heat transfer, friction, blow-by and overall energy distribution.

The material change therefore affects much more than mechanical strength.

Oil-Jet and Gallery-Cooled Pistons

High-output engines frequently spray engine oil against the underside of the piston crown.

This removes heat from one of the most thermally loaded areas of the engine.

Highly loaded diesel pistons may go further by incorporating an internal cooling gallery.

Oil enters the gallery and oscillates as the piston reciprocates, creating a shaker-cooling effect.

Correctly designed piston cooling can substantially reduce critical temperatures around the crown and combustion-bowl rim.

Piston Surface Treatments and Coatings

Modern piston performance is not determined exclusively by the base alloy.

Specific areas can receive specialised surface treatments.

Skirt Coatings

Low-friction skirt coatings are designed to:

• reduce friction;

• control scuffing;

• reduce skirt wear;

• improve break-in;

• reduce piston noise.

MAHLE's graphite-based GRAFAL skirt treatment, for example, is used to reduce friction, scuffing, cylinder wear and piston noise.

Phosphate Coatings

Phosphate treatments can provide temporary lubrication and anti-galling protection in areas including the pin bore and ring grooves during initial operation.

MAHLE uses such treatments to reduce the risk of pin galling and ring-groove microwelding.

Hard Anodising

Hard anodising may be applied to critical regions such as the top ring groove.

The aluminium surface is converted into a hard oxide layer, improving resistance to wear and microwelding.

It is particularly useful where ring-groove temperatures and pressures are severe.

Thermal-Barrier Crown Coatings

Ceramic thermal-barrier coatings are sometimes applied to piston crowns in competition engines.

Their purpose is to reduce heat transfer into the piston.

However, this should not automatically be considered an upgrade.

Reducing heat transfer into the piston means more thermal energy remains within the combustion chamber and exhaust gases.

That can alter:

• combustion-surface temperature;

• exhaust-gas temperature;

• knock tendency;

• turbocharger thermal loading;

• valve temperature.

Thermal-barrier coatings therefore need to form part of the complete thermal strategy of the engine.

How RPM Changes Piston Requirements

High RPM creates enormous inertial loading.

The piston must accelerate from zero velocity near top dead centre, reach extremely high velocity around mid-stroke and decelerate back to zero within milliseconds.

Piston acceleration rises approximately with the square of engine speed.

Consequently, increasing engine speed from 7,000 to 8,000 rpm does not merely increase inertial loading by 14%.

The change is far more significant.

Reducing reciprocating mass can therefore have major benefits in high-RPM engines.

But reducing weight without maintaining stiffness can cause:

• piston distortion;

• pin-boss deformation;

• ring-groove movement;

• fatigue cracking.

Lightweight design and structural integrity must be engineered together.

How Cylinder Pressure Changes Piston Requirements

Turbocharging primarily increases piston stress by increasing cylinder pressure and heat release.

Higher peak cylinder pressure places additional load on:

• the crown;

• ring lands;

• piston pin;

• pin bosses;

• connecting rod;

• crankshaft;

• bearings.

Very high boost therefore does not automatically require the lightest possible piston.

It may require additional crown and pin-boss structure even if this increases piston mass.

The optimum piston for a high-RPM naturally aspirated engine may consequently look very different from the optimum piston for a high-boost turbo engine.

Detonation and Piston Damage

Detonation produces extremely rapid pressure oscillations after ignition.

These pressure waves can dramatically increase local mechanical and thermal loading.

Common piston damage associated with severe abnormal combustion includes:

• broken ring lands;

• collapsed ring grooves;

• crown erosion;

• melted crown edges;

• damaged pin bosses;

• skirt damage.

Pre-ignition can be even more destructive because combustion begins before the commanded spark event, potentially causing enormous pressure while the piston is still approaching top dead centre.

A forged piston provides increased mechanical margin, but no piston material can compensate indefinitely for incorrect engine calibration.

Selecting the Correct Piston for the Application

Standard Road Engine

Priorities generally include:

• low noise;

• low oil consumption;

• emissions;

• long service life;

• tight cold clearance;

• cost efficiency.

A well-engineered cast aluminium piston is often the ideal solution.

High-Performance Road Engine

Priorities shift towards:

• increased cylinder pressure;

• increased thermal loading;

• durability;

• reasonable NVH;

• long road service.

A 4032 forged piston can be particularly attractive where additional strength is required without sacrificing tight cold clearance.

High-Boost Turbo Engine

Important requirements include:

• crown strength;

• ring-land integrity;

• high-temperature capability;

• pin-boss strength;

• abnormal-combustion tolerance.

2618 forged pistons are therefore extremely common in this category.

High-RPM Naturally Aspirated Racing Engine

Here the priorities can include:

• minimum reciprocating mass;

• high fatigue resistance;

• thin ring packages;

• compact compression height;

• high-strength pin design;

• optimised skirt area.

Piston geometry can become just as important as material choice.

Endurance Motorsport

Endurance racing creates a different problem from a short qualifying or drag-racing engine.

The piston must withstand not only maximum load but millions of high-temperature fatigue cycles.

Thermal stability, ring-groove wear, lubrication and cooling therefore become critical.

High-Output Diesel Engine

Extremely high cylinder pressures and combustion temperatures may eventually exceed the practical limits of aluminium.

Steel or composite piston construction then becomes increasingly attractive.

Modern diesel piston development reflects exactly this trend.

Forged vs Cast Pistons: Which Is Better?

There is no technically valid universal answer.

A high-quality cast piston may be better for a production road engine because it can provide:

• excellent dimensional stability;

• quiet operation;

• low oil consumption;

• long life.

A forged 2618 piston may be better for a heavily boosted competition engine because it provides:

• greater toughness;

• increased ductility;

• improved tolerance of severe mechanical loading.

A 4032 forged piston occupies a useful middle ground where additional strength is required alongside good dimensional stability.

And when cylinder pressures become sufficiently extreme, steel may become more suitable than either aluminium option.

The question should therefore never simply be:

"Is forged better?"

The correct engineering question is:

"Which piston material, geometry and manufacturing process provides the required fatigue strength, thermal behaviour, clearance, mass and durability for this particular engine?"

Final Engineering Perspective

A piston represents a compromise between conflicting requirements.

It should ideally be:

• light;

• strong;

• stiff;

• ductile;

• thermally stable;

• highly conductive;

• wear resistant;

• low friction;

• quiet;

• inexpensive.

No single material maximises all of those properties simultaneously.

A low-expansion high-silicon aluminium piston provides different advantages from a ductile 2618 forging.

A 2618 motorsport piston provides different advantages from an OEM cast piston.

A steel diesel piston addresses an entirely different combination of cylinder pressure, temperature and durability requirements.

Correct piston selection therefore begins with understanding the engine's intended operating envelope—not simply selecting the component advertised as the strongest.

For performance engines, piston specification should be considered together with compression ratio, boost pressure, ignition strategy, fuel quality, combustion temperature, ring package, piston cooling, bore material, connecting rods and intended duty cycle.

That system-level approach is what separates proper engine engineering from simply fitting performance components.

Frequently Asked Questions About Engine Pistons

Are forged pistons stronger than cast pistons?

Generally, a properly engineered forged piston provides greater mechanical strength and toughness than a conventional cast piston of comparable design. However, alloy composition matters enormously, and modern cast pistons can be extremely capable in their intended operating range.

Is 2618 better than 4032?

Neither alloy is universally better. 2618 offers greater ductility and is widely used for severe racing and high-boost applications. 4032 contains much more silicon and provides lower thermal expansion, allowing tighter clearances and quieter street operation.

Do forged pistons need more clearance?

Not simply because they are forged.

The required clearance is heavily influenced by the alloy.

A forged 2618 piston normally requires greater cold clearance than a forged 4032 piston because 2618 experiences greater thermal expansion.

What is a hypereutectic piston?

A hypereutectic aluminium-silicon piston uses an alloy with silicon content above the aluminium-silicon eutectic composition. The high silicon content reduces thermal expansion and improves wear behaviour.

Why are racing pistons often made from 2618?

2618 combines high strength, toughness, elevated-temperature performance and ductility, making it particularly suitable for engines subjected to very high cylinder pressure and severe competition duty.

Why are steel pistons used in diesel engines?

Steel provides much greater mechanical strength and lower thermal expansion than aluminium. These characteristics become advantageous as diesel cylinder pressures and thermal loading increase.

Can forged pistons stop engine knock?

No.

Piston material cannot prevent knock or detonation. Combustion control comes from appropriate fuel octane, ignition timing, boost pressure, air temperature, mixture preparation and engine design.

A stronger piston may survive abnormal combustion for longer, but it does not eliminate its cause.