Why tuning with AFR?
Adjusting the LPG system on the road by measuring AFR is a complete LPG setting. It is to adjust the LPG system of the vehicle to be exactly with these values by reading the fabricated air / fuel mixture ratios in the gasoline of the vehicle (with the help of Wideband AFR sensor) and using it under different conditions while driving.
AFR tuned LPG vehicles;
Now let’s continue for a detailed explanation:
For the question of why we need to do AFR with the sensor, let’s first try to explain what the terms mean.
+++ What is Lambda, AFR?
This shows how many units of air have entered the cylinder for one unit of fuel for combustion. For example, 14.7 AFR means burning with 14.7 units of air to 1 unit of fuel. As this value increases, that is, as the rate of air in the mixture increases, we use the term “poor” for the mixture and “rich” as the air ratio decreases.
Our vehicles are set to operate at fixed speeds such as a closed loop, ie quarter gas, or at Stoichometric air fuel ratio in unloaded usage. If the need for acceleration is at full throttle, the ECU switches to open-loop state. They slightly enrich the air fuel mixture. There is no reading and correction by means of oxygen sensors. Since the oxygen sensors in the vehicles are narrowband sensors, they cannot read exactly in these parts.
In the table, we see the various combustion rates and what kind of conditions (economy, environmental, power) the mixture is changed when desired.
LPG fuel gives the desired and received stoichometric properties (desired emission, temperature, power amounts) at a rate of 15.5 in gasoline in a mixture of 14.7. In other words, when the sensors give the value of lambda 1.00 in use with LPG fuel, our mixture will be 15.5. For LPG, lambda corresponds to 1.00 = 15.5 AFR.
+++ What is EGT?
EGT (Exhaust Gas Temperature) It is the exhaust gas temperature. After the fuel is burned in the combustion chamber, the exhaust smoke temperature changes according to the mixture. Why is this value important to us? Because the exhaust gas temperature rises very high in the lean mixture, and it will cause the parts that are in contact with the exhaust gas to be exposed to intense heat. This causes the exhaust valves that discharge this gas to melt. If you pay attention, it will be seen that the exhaust valves of the vehicles whose valves are melted are always melted.
The reason why this melting-elongation is fast in LPG vehicles is the poor mixture due to completely unbalanced operation. Poor combustion at high loads causes exhaust valves to melt prematurely.
+++ What is a Catalytic Converter?
A catalytic converter, or catalytic converter, is the device that converts environmentally harmful substances in engine exhaust (the gas they exhaust) into less harmful substances. This converter is located in the form of a honeycomb at the exhaust outlet. It ensures that we do not harm the nature by separating carbon monoxide into less harmful and recyclable Carbon dioxide gas with various elements (platinum, palladium or rhodium) and highly toxic Nitrogen oxide gases into Nitrogen and Oxygen.
In new generation vehicles, there is an oxygen sensor at the outlet of this converter and it measures the state of waste gases. If the floor converter has become unable to perform the operation, your vehicle will turn on a fault lamp.
The Catalytic Converter is a long-lasting part. As long as a motor is working properly, it will not cause any problems for a long time. If there is a problem, there are 2 reasons.
– The first is that the vehicle is constantly used for short distances, bad fuel, raw fuel or oil deposits due to oil burning passivate these active substances, and the converter changes its state.
– The second is that the high EGT temperature caused by unbalanced combustion melts these active substances in the catalytic converter, melting, cracking or breaking inside the layer converter.
We usually see the 2nd situation in vehicles with unregulated LPG. Again, the high EGT resulting from the poor mixture, which we will mention in the open-loop, melts these elements in the catalyst while melting the valves.
+++ What is a Closed Loop?
Closed-loop driving is the situation that occurs when our vehicles are not loaded at full throttle during use. Oxygen sensors located at the exhaust outlet of our vehicle continuously inform the vehicle brain (ECU) and the mixture is kept constant at LAMBDA = 1.00. This ratio corresponds to 14.7 in gasoline and 15.5 in LPG.
If the fuel is too much or less during the closed loop, the vehicle brain sees this from the oxygen sensor and corrects it by increasing / shortening the injection time. Accordingly, it records LTFT (Long term fuel correction data) and STFT (Short term fuel correction data). If the LPG installation setting is broken in the closed loop, the vehicle can overcome this part by fuel correction. However, in vehicles with extremely bad adjustment in LPG, this correction reaches and passes up to 25%. After this point, the vehicle warns its driver by lighting a malfunction warning lamp because it fails despite trying to make a correction. In other words, it is not an easy task to illuminate the fault lamp in an LPG vehicle, this indicates an extremely bad setting.
+++ What is an Open Loop?
Open-loop driving is the situation that occurs in our engine when our vehicles require acceleration or full power. Our engine does not make fuel correction with the oxygen sensor at such moments and enriches the mixture.
According to the measurements we made with Wideband (broadband / broadband reading) Oxygen sensor, for example;
Atmospheric engine vehicles burn with 12.5 – 13.0AFR according to measurements at full gas.
Turbocharged vehicles can go further down, for example; The 180 hp Insignia with A16LET engine accelerates at full throttle, and burns with 11.5AFR in case of overboost with 1.3 bar turbo pressure.
Here is the problem with LPG installation. This part (full throttle part) remains a complete mystery in the LPG fuel map part, as it cannot be measured neither by road adjustment nor with the fuel correction data of the vehicle brain. What needs to be done is to see how many AFR / Lambda values the vehicle gives in gasoline use in full throttle / open-loop position by means of the broadband sensor, then take the vehicle to lpg and set the vehicle to the equivalent AFR / same Lambda value in lpg at full throttle / open-loop position.
When the LPG adjustment is made in this way, it will realize the healthy combustion of LPG in engine gasoline, and there will be no conditions such as low performance, valve melting, catalytic converter melting.
+++ Misunderstandings / Frequently Asked Questions
Question: Are valves not melting because of the high combustion temperature of LPG?
Answer: The problem is not the combustion temperature of LPG. LPG’s burning calorific value is only 4.8% higher than gasoline. This is not an excess that will cause any deformation in the valves or the engine.
Let’s evaluate this proposition from two sides. The first is a gasoline solvent. We use gasoline to dissolve grease and dirt on an oily part, a dirty part. It is absurd to think that gasoline is lubricating when such a situation exists.
The second aspect is that the valves with which gasoline comes into contact are intake valves. Melting valves are exhaust valves where the fuel does not come into contact from the top.
Question: Is there a difference in compatibility between LPG systems and vehicles?
Answer: All inline LPG kits contain the same main elements. ECU (Electronic control unit), Regulator, Injectors. The work they do is the same. There are various kits available in a wide price band. Of course there are differences between them in terms of material quality. But it is the assembly and adjustment quality that makes a kit compatible with the vehicle. That is to say, while a well-adjusted average kit can get results indistinguishable from gasoline, the quality of the material sold at very high prices in the market will not be achieved if a kit is not correctly assembled and adjusted precisely with the sensor. So, as is the case with most tools, the skill is in the user / driver, not in the device. The setting that drives the kit is also.
Question: Can the lubrication systems in LPG kits prevent valve melting?
Answer: This proposition should also be considered from various angles. First of all, the valves that this oil touches will be intake valves and there is no melting in these valves. The second part is known in vehicles that oil is not required to enter the combustion chamber, oil burning is the biggest enemy of a vehicle. According to the findings, these lubrication systems are:
It causes unwanted things like. In short, this oil to be supplied with the fuel in the manifold will not have any positive benefits and there is a risk of damaging various parts.
Question: Is LPG fuel harmful to the engine due to its nature? What are the things to watch out for?
Answer: LPG fuel is a fuel that is beneficial to the engine and the environment compared to Gasoline under the same burning conditions with the correct setting.
In the light of all this information, we can say that the engine of an LPG vehicle that is correctly adjusted and working properly with all its equipment will have a longer life.