Exhaust Temp: Engine Load Indicator?

Hello everyone,

I have a question, especially for the professional mechanics (but also for everyone else). A friend of mine has a Land Rover Discovery TDI, and when he was looking online for tuning options, he came across a website that goes into quite detail about modifications to the ESP, increasing boost pressure, etc. Besides the maximum acceptable boost pressure and soot emissions, the author believes that the exhaust gas temperature is a key indicator of engine stress or overload. He even argues that monitoring the exhaust gas temperature (which isn't exactly cheap) is essential for more extensive tuning. What do you think about this? Has anyone ever considered or done something in this direction?

Best regards, Frank.

Hello Frank,

"Exhaust gas temperature is monitored, for example, in aircraft engines. However, these are all gasoline engines, either turbocharged or naturally aspirated. The monitoring of exhaust gas temperature serves to optimize the air-fuel mixture for maximum efficiency, as this does not happen automatically in older engines and must be adjusted based on external pressure and temperature. Because a gasoline engine requires a stoichiometric (Lambda = 1) air-fuel mixture, it is possible to operate with an optimal exhaust gas temperature even under partial load. (The mixture is initially set for the maximum exhaust gas temperature, then slightly enriched to achieve better internal engine cooling)."

In my opinion, the lambda value plays a minor role in diesel engines. The exhaust gas temperature is likely to be much more dependent on the engine's power output, similar to gasoline engines, because lean air-fuel mixtures are used at partial load.
(And then there are things like AGR).

The exhaust gas temperature is certainly important for the turbocharger, as it drives the turbine, and the thermal stress limit of the turbine must not be exceeded.

I don't think it's suitable as the sole parameter for evaluating a turbo diesel tuning modification.

The monitoring doesn't necessarily have to be expensive. The thermocouples should be suitable for the application.

Perhaps we have an expert in engine development among us who knows more.

Best regards,
Christian.

Frank A. wrote:

Hi @ all, The author believes that the exhaust gas temperature is a key indicator of stress or overload on an engine. He even argues that monitoring the exhaust gas temperature (which isn't cheap) is essential for more extensive tuning modifications. What do you think about this? Has anyone ever considered or implemented something like this? Hi Frank

HI!

Okay, so expensive the exhaust gas temperature monitoring isn't. As far as I know, it's even used in go-karts. But I wouldn't say that the main purpose here is to monitor for overload. It's primarily important to control the temperature to detect excessively high temperatures early on, which often points to a too-lean fuel mixture.
In some racing engines, even up to 4 temperature sensors were used.
'I need to monitor all four cylinders because they were supplied with different fuel mixtures. However, I don't really know much about diesel engines.'

Greetings!

hello

'I've been working at Delphi in the engine testing and development department since September of last year, and I'm gradually getting more involved in the subject matter. Before this, as a mechanic, I didn't have much experience with engine testing, or only had a superficial understanding of it.'
Since I'm directly involved with the engines, I can say that during testing, we monitor the exhaust temperatures of each individual cylinder, as well as the turbocharger inlet and outlet. (By chance, we currently have a diesel engine, which is particularly interesting for me personally, since I own a TDI myself).
I also inquired about temperatures as an indicator for tuning, and it turns out that the intake air temperature measured directly at the turbo should not exceed approximately 190°C. This is a general guideline. However, the temperature only indicates the load on the turbocharger, but not necessarily the direct load on the engine. While you can get some idea from the temperature, it's not very precise. The problem is that you also need to consider the combustion pressure, which is actually the critical factor. This varies depending on factors like fuel injection amount and timing, etc.

The temperature measurement itself is not particularly expensive or complicated. You can even use readily available tools, such as a multimeter with temperature measurement capabilities and simple temperature sensors. We use ones with a diameter of 1 or 3 mm, for example, which are also available at Conrad.
It's also interesting to measure the lambda value in a diesel engine because it can reveal how the fuel injection量 relates to the amount of air – whether too much fuel is being injected or if more could be added.


Best regards, ixery.

HI,
Assuming corresponding reference values are available, I can start to make sense of the temperature data.
"Standard tuning methods, whether using a chip or a module, increase the amount of fuel injected by extending the injection duration. The later the fuel is injected, the worse the engine's efficiency becomes. Consequently, an increasing amount of the fuel's energy remains in the exhaust gases."
Even if excessive soot production didn't limit the injection duration, an excessively long injection time would eventually cease to result in any further performance gains.
The exhaust gas temperature, which increases significantly, is easier to determine than the specific fuel consumption, which also increases.

The charging infrastructure is unlikely to be at risk for diesel vehicles anytime soon.

The charger is unlikely to be at risk with the diesel engine.

Recently, a university conducted a tuning test and found that some chips/boxes caused significant exceedances in exhaust gas temperature at full load for certain vehicles.
This means significantly above 850°C.

Could the VTG (Variable Turbine Geometry) soften or deform under constant full throttle?

CU Gremlin.

Hi,
850°C is indeed quite high. The charger is certainly not designed for that temperature. Neither is the turbine rotor built to withstand it for long. While there are alloys that can handle it, they probably wouldn't be used if it's not necessary under normal operating conditions. The problem then becomes the material's resistance to prolonged exposure at those temperatures; running at full throttle continuously will eventually lead to failure.
I don't know whether ceramics are currently being used, as it's been too long since I last worked in that field.
What happens to the bearings when you shut off the engine without letting it idle first won't be good either.

Temperatures of 750°C should generally not be exceeded, and if they are, only for a short period. The vtg material is not designed to withstand such high temperatures for extended periods.



ixery

Deleted upon request.

However, it is very unlikely that such temperatures will be reached for more than a few minutes during normal driving conditions. Every time the accelerator pedal is released, the exhaust gas temperature in a diesel engine drops very quickly.



[ ] do you know how to get a 66kW TDI engine to achieve an average fuel consumption of 8.7 liters?

CU Gremlin.

Gremlin wrote:

Do you know how to get a 66kW TDI engine to achieve an average fuel consumption of 8.7 liters?

... but I can certainly compete with that: 11.5 liters per 100 km average fuel consumption for my car, which has a 74 kW engine (and I also own an apartment in the Netherlands, thanks to the "Jeanette" autumn storm) .