A brief analysis of the differences between aviation and automotive piston engines

From a principle point of view, there is no essential difference between aerospace piston engines and piston internal combustion engines widely used on the ground, and their development also depends on the technology of ground internal combustion engines. However, due to the different use occasions and environments, there are obvious differences between aviation and automotive piston engines.

1. Common types of aviation piston engines:

1) Inline (liquid) air-cooled engine

In 1903, the Wright brothers in the United States modified a 4-cylinder inline water-cooled engine and successfully used their "Flyer One" aircraft for flight tests. This engine only emits 8.95kW of power, but weighs 81kg.

2)V-type engine

Just put everythingcylinderIn two groups,The adjacent cylinders are arranged at a certain angle, and the cylinders are seen from the sideV-shaped engine. Its characteristics are light weight, length and size. With the increasing progress of technology, its power has increased significantly and has been widely used in the automotive field.

3) Star engine

Generally, the number of cylinder groups of star engines is odd, there are5 cylinders, 7 cylinders, 9 cylinders, in order to increase power, they can be stacked with multiple rows, and multiple cylinder groups are arranged into several rows, more than 4 rows × 7 cylinders (28 cylinders), and are rarely used at present.

Image source from the Internet

4) Horizontal opposing engine

Its characteristics are compact structure, high power weight, high reliability, great power improvement potential, good maintenance and survival. It can also reduce the windward area and drag of the aircraft. It is currently the mainstream type of aviation piston engines.

Currently, most aero piston engines use inline and horizontal opposite engines.

Picture HaeryDB883Horizontal opposing engine The picture isDB416 horizontal opposing engine

2. The main technical characteristics of aviation piston engines (main differences from automotive use):

1) Aviation piston engines have relatively reliable and safety requirements

① Based on the use environment and working conditions of the aero piston engine, low-temperature trusted start technology is adopted. Its key technologies include:

Cold start preheating technology;

Cold start electronic injection control technology;

Starter speed drag technology.

It is mainly achieved by increasing the air temperature after the engine is compressed, increasing the fuel temperature, optimizing the fuel injection parameters in the starting stage and improving the engine drag speed. In order to ensure that the engine can be started with a reliable starting capacity in a relatively empty and colder environment.

② In accordance with the requirements of airworthiness certification of laws and regulations, adopt redundant safety design. To give a few examples:

Aviation engines usually use independent double ignition systems (double spark plugs) and dual magnetomotors; this is not the same as the purpose of automotive engines using double ignition;

The aviation heavy oil engine adopts a dual injector design;

The electronic control system adopts dual sensors and redundant design; (for example: the fuel metering valve of the fuel system is used in combination with the oil rail pressure relief valve, so that the aircraft still has certain power to return to land after the fuel system fails)

engineThe FADEC system also adopts a redundant design;

Double and multiple launches are also reflections of the principle of redundant design on aircraft.

2) The weight requirement of aviation piston engines is "focused"

In terms of design, lightweight design is generally adopted. Under the requirements of strength and stiffness of parts, unnecessary parts are removed and innovations and applications in new materials, new processes and new structures are carried out. for example:

Many small drone engines do not have a start system, and some drones have selected low-speed engines (no deceleration system) due to their purpose and actual aircraft.

For traditional steel parts (such as crankshafts, connecting rods, bolts, nuts, etc.), titanium alloy materials with better strength are used;

By using a new process of spraying wear-resistant layers for cylinder bores without cylinder liners, we can replace the traditional iron cylinder liners to achieve the purpose of friction and weight reduction;

Adopt lightweight structure design such as weight reduction holes, hollow crankshafts, hollow camshafts, etc., and useCAE tools optimized component strength and stiffness requirements for weight reduction;

The picture is HaeryDB201engineThe picture is HaeryDB403 engine

The weight of the engine is one of the key considerations for drones

3) Aviation piston engines pay great attention to the relatively empty performance of the engine

This is mainly determined by the particularity of the engine's use environment.

For example: the change of the engine's main power indicators with the increase in flight ratio (based on the aircraft's flight envelope); the change of the engine's fuel consumption indicators with the increase in flight ratio (liquid state and oil-rich state)

Sometimes, in order to reduce the performance attenuation of lesser and ultra-empty engines, multi-stage supercharged intercooling technology is also used in the design.

4) Aviation piston engine must be matched with the propeller

Propellers are loads in operation of aviation piston engines, so the engine must match the characteristics of the propeller to select.

There are two common propellers:

Fixed slurry torque propeller (fixed slurry, simple and light in structure)

Adjustable torque adjustable propeller (moment variable propeller, good adaptability and heavy)

5) Many tests for aviation piston engines must be carried out in a slurry state, that is, a propeller test bench must be established. If it is a helicopter engine, it is better to have a rotor test bench.

It mainly verifies the better propeller engine matching and tests the main performance of the engine under actual load.

Image source from the Internet

6) Unique lubrication system

Since aircraft are flying in various postures, normal flights include climbing, dive, rolling, left-tilt, and right-tilt, and in special circumstances, abnormal tail rotation will also occur, so aviation piston engines generally use a dry lubrication system for lubrication function. Some products also use fuel lubrication technology, self-lubricating bearing technology, friction resistance reduction and wear resistance technology.

Today, the editor will give you a brief introduction:

Fuel lubrication technology uses the pressure and branch circuits used in common rail systems to inject atomized fuel into the crankcase, and uses scavenging gas to assist in lubrication of moving parts. This lubrication method is generally used more frequently in two-stroke engines, but a small amount of lubrication injected into the crankcase will enter the cylinder through the sweeping air duct, which will increase fuel consumption and affect combustion stability. Therefore, the application of this technology must combine the characteristics of electrical control and adjustable, and quickly control the dose and supply time of lubricating branch;

Self-lubricating bearing technology uses wear-resistant and temperature-resistant self-lubricating bearings. For the lubrication of moving parts at faster and higher temperatures, it is reliable. In the end, for the main bearing, cam bearing, connecting rod big head bearing and other moving parts have good lubrication performance;

Friction resistance and wear resistance technology are generally used more frequently in piston rings and crank journal positions. The purpose of reducing the overall friction resistance through low elasticity, crankshaft small journal design, low friction coefficient coating application and lubrication system optimization, improve the mechanical efficiency of the system and reduce fuel consumption.

7) has relatively engineering maintenance

In order to consider the portability, low cost and low time consumption of customers during use, we choose the fast plug-in start module design, modular quick change technology of the whole machine, and the maintenance optimization technology.

8) Real-time health diagnosis technology

On the basis of communication with aircraft avionics systems, the electronic control system of the aviation piston engine must also have real-time health self-diagnosis technology and communication with the Beidou system. Its purpose is:

Through health self-diagnosis technology, pilots and ground clients can master engine operating parameters to a greater extent. When the parameters are abnormal or deviate from the target, the electronic control system realizes parameter deviation correction through relevant signals and related control models, forming closed-loop control of engine abnormal points, in order to adapt the engine operation to the environment;

The engine diagnostic data, operating status data and operating status data are transmitted to the ground client in real time through the Beidou satellite.

Summarize:In the research and development process of product design, simulation calculation, experimental development, etc., aviation piston engines should pay more attention to the differences in ground and air use, be familiar with the basic knowledge of aviation, the airworthiness certification process and requirements, the technological development and characteristics of related industries, and customer pain points, in order to develop products with excellent quality and satisfactory customers.