Liquid cooling vs Oil cooling vs Air cooling which is the best and why?
– Bhagwan Hindustani
We all know how important engines are for an automobile as these are the prime drivers and our vehicles essentially won’t move without engines. Even with the advent of Electric vehicles and with world countries looking to end their dependency on fossil fuels by moving away from regular petrol and diesel to more environmental friendly alternatives, Internal Combustion engines are here to stay at least for another three decades or even more.
Companies around the world are working their ways to actually make the IC Engines more environmental friendly and efficient. One of the main components of the engines that actually help them to be more efficient and environment friendly is the cooling systems the engines employ. Cooling systems are one of the essential parts of the engine making the engine last longer by venting out the extra heat to the atmosphere and also saving the parts of the engine from being destroyed. Cooling systems are very important as more than half of the heat energy produced by the engines is carried away by the coolant system and only 20 to 40 percent of the heat energy is used to run the vehicle.
Before diving deep into the types of cooling systems, their respective advantages and disadvantages, let’s take a look at different functions performed by the cooling system.
- Cooling system removes excess heat from the components and protects them from excessive thermal expansion, thereby increasing their life time.
- Cooling system also decreases the occurrence of uncontrolled combustion in both diesel and petrol engines which is called as “knock”. Knock is basically a pre-ignition phenomenon causing damage to the engine parts.
- Effective cooling system actually helps in achieving higher compression ratios and thereby increasing the efficiency of the engine.
- Cooling system also helps in controlling emissions. At 1500 degree Celsius, Nitrogen in the air reacts with oxygen and forms Nitrous Oxide which is an issue with diesel engines as they can run high compression ratios and generate more heat. So keeping the combustion chamber’s temperature below 1500 degree Celsius is a must for diesel engines.
The above listed functions are some of the most important functions performed by the cooling system. There are mainly three types of cooling system that are currently used in the automotive industry.
- Air cooling
- Liquid cooling
- Oil cooling
- Air and oil cooling combined.
- Air cooling
Air cooling is probably one of the most used and simplest cooling systems which are currently available in the automotive industry. As the name suggests, the excess amount of heat produced by the engine is carried away by air flowing over the engine. In order to increase the heat transfer efficiency of the engine, “Fins” are provided on the cylinder block. This is done to increase the area of heat transfer so that heat will be transferred effectively to the atmospheric air.
- Air cooling systems add a lot more weight to the engine compared to other cooling systems as it require metal fins to carry our effective heat transfer. More metal means more weight.
- At higher air temperatures, heat transfer might be affected.
- Air cooled engines generally produce lower power and torque figures than their liquid cooled counter parts as they can’t risk the generation of higher temperature leading the engine parts to fail eventually.
- For example, a Cummins liquid cooled engine which can generate 450 bhp needs only 8000 cc of engine capacity compared to a Tatra air cooled engine which needs 12,996 cc for generating the same amount of power as the Cummins engine.
- Meeting emission requirements with air cooled engines are quite a challenge. Though for military vehicles, emission standards doesn’t apply.
2. Liquid cooled:
- Liquid cooling is one of the advanced cooling systems that are being used in auto industry today.
- Almost all passengers cars today in our market come equipped with liquid cooling.
- In liquid cooling, the engine components are cooled via liquid flowing through the chambers that will be made around the cylinder blocks and in the engine head.
- Liquid cooling enables the use of higher compression ratios as it can protect the engine parts effectively from over-heating.
- Engines equipped with liquid cooling can generate same power as an air cooled engine with larger engine capacity.
- Liquid cooling can help in the weight reduction of the engine and also helps in achieving emission goals easier than the liquid cooled engine.
- Liquid cooling requires regular maintenance as the coolant level needs to be checked and added if the minimum level comes down.
- Liquid cooling involves using pumps and radiators so chances of a mechanical failure are a bit more compared to liquid cooling.
- If the head gasket blows, there a chance that the liquid coolant might leak into the combustion chamber and causes white smoke.
Oil cooling is very similar to liquid cooled engines and the working principle of the oil cooled engines is more or less the same as liquid cooled engines. So oil cooling won’t be explained in details in this article.
In recent years, many companies like Bajaj and Royal Enfield have implemented a hybrid cooling system where the engine uses both oil and air cooling systems in tandem. This hybrid system strikes a balance between liquid and air cooling and still has less manufacturing costs.
Liquid vs Air cooling and its genesis:
The argument of liquid cooling vs air cooling started a few days before when BEML unveiled a new truck they were designing and mentioned the engine to be an air-cooled V8 engine which can generate up to 438 bhp. This particular vehicle will be equipped with Tatra’s (supposedly) new range air cooled heavy weight diesel engine.
Social media gave mixed reactions to this post. Someone said “when the engine is doing great and is even deployed in Thar Desert, then why not use it.” Whereas some other said that why use an air cooled engine in the ear of liquid cooling when passenger vehicles come with liquid cooling.” Let’s dive into the arguments one by one.
Argument – 1
Tatra has been making air cooled engines for a while now. These air cooled engine even meet the Euro – 5 standards.
Yes, Tatra has been making air cooled engine for a while now and they even meet Euro – 5 standards. But when an engine can be made as powerful as the air cooled engine with arguably 40% less weight and improved thermal efficiency then why not use liquid cooled engines. We all know that more the weight of vehicle , more the inertial will be and more fuel is consumed by the vehicle affecting the range.
Argument – 2
Tatra uses air cooling system because it wants to keep the maintenance low and also it can be easily repaired by local mechanics. If a system can be so simple, why complicate it by adding moving parts?
Agreed that air cooled systems are simple to operate and maintain but it’s not like Tatra will be first Truck Company in the world to use liquid cooling. Other army trucks from the stables of Mahindra, Ashok Leyland and Tata all use liquid cooled engines. Most of the mechanics are fairly knowledgeable and confortable working with liquid cooling systems. And now-a-days, liquid cooling systems have become fairly reliable and advanced and even environmental friendly.
Adopting an already available and mastered technology isn’t a difficult task. According to my personal opinion, using air cooled engines especially for trucks and heavy duty vehicles these days is like using a Nokia 1100 in this era of more advanced smartphones which are both reliable and does the job very well. For sure Nokia 1100 works till today. But it misses out a lot of functionality the modern day cell phones have.