Biofuels in Diesel Engines

  • #1
First let me say hello and give an introduction.

I have limited academic experiecnce in Physics receiving a C-grade GCSE at 16.

I then spent over a decade owning a maintaining a number of motorbikes, cars, and light and medium commercial vehicles and some light plant machinery. Mainly for myself for transport and as a self employed gardener /tree surgeon but also helping friends and relitives with their vehicles.

At the end of 1999 I read the book 'From the fryer to the fuel tank' about fuelling diesel engines with vegetable oil and biodiesel and rapidly got sucked into spending far to much time researching the use of vegetable oil as a fuel.

I set up an information website at[/url] and later started working at [url][/URL] where I provided the in house expertise on vegetable oil combustion. I held a directorship at this not-for-profit co-operative before leaving last summer.

Since leaving I have continued my experiments and research into fuelling engines with vegetable oil (aka PPO)

I am interested in anybodies thoughts on this subject.

I was also wondering if I could get some guidance.

One of my current projects involves gathering a number of sensors and hooking them up to my laptop to log pertinent data that will allow me to tune engines to run on PPO. I am at an early stage but am following 'crossbones' somewhat pioneering work (as far as I am aware) using glowplugs as a combustion chamber temperature feedback sensor. (see [url][/url] )

The first vehicle I'm working on is my 1994 Mercedes 310D mechanical in-line injector pump. (as I use it the most)

Sensors I plan to use.

block temp (from coolant drain plug on the engine block)
air inlet temp
fuel temp (I will be heating the fuel)
rpm (either using a magnet and reed switch or photoreflector?)
mph (as above)
injection time (using piezo crystal high pressure clamp)
I'd also like to get some kind of combustion/knock sensor working

My criteria for sensor selection are I am on a very limited budget, the sensing equipment should be reasonably easy to mount (I want to be able to move this from one engine to another) and ideally the equipment would be durable on a road going vehicle used in all weather conditions.

After a bit of research I spent out on what I think is a reasonable interface/software combination to enable me to get some good data - a LabJack Pro UE9 which comes with DAQFactory Express. ( [url][/url] )

Any suggestions of suitable equipment or other data points that would be worth collecting would be appreciated.

Sorry for the rambling post...:rolleyes:

Best regards

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Answers and Replies

  • #2
To be able to get a really good tune out of the engine, you'll need both a way to adjust the fuel map of the engine, and you'll want to be able to monitor the air/fuel ratio in the engine using a Wideband Oxygen Sensor in the exhaust before the catalytic converter(s).

By monitoring the AFR in the engine, you can see exactly where you are, and where you'll want to be to make peak power. Additionally, you'll probably want an EGT gauge as Diesel's EGT's will go off the charts if you pump enough fuel in the cylinders.

Doing a search online should get you some good data on high performance AFR's for diesel engines, as well as stoichiometric values. That, and how you can adjust or fake out the engine's ECU will be a good place to start.
  • #3
Hello Mech_Engineer,

I am not looking for a high performance tune just to optimise combustion with a different fuel.

As I understand it (I could be wrong) EGT and AFR would only be necessary if I wanted to change the fuelling for top end performance. I have the glowplugs which I'm using to read relative temperature in the cylinders.

What I would like to find is a source of reasonable quality / reasonable price glow plug pressure sensors. Or another reliable/easy/cheap method of seeing the combustion event. Anyone got any ideas.


  • #4
I don't really see how combustion pressure or temperature readings will help you in your quest, unless you plan on changing the compression ratio of the engine. What modifications do you actually plan on doing to the engine?

As far as I know, diesel engines run quite well off of biodiesel without any modifications at all. It's possible that biodiesel's stoichiometric AFR is slightly different than regular diesel, but you have no way of reading or changing that through cylinder pressure or temperature.
  • #5
Sorry I should of prehaps made things a bit more clear. I'm looking at optimising engines to run, not on biodiesel, but pure rapeseed oil (and in future other plant derived oils and fats). Use of these fuels is growing in Europe and the US but it is still a niche and good information on combustion is not readily available.

The link at

explains a fair amount about using the glow plugs as a relitive temperature feedback to allow timing to be optimised (in short get lowest temps with the same performance)

cylinder pressure readings would be usefull to show the true combustion time which changes with fuel due to injection lag and ignition lag. It would also show the burn rate.

I found this interesting thread

which had a particularly interesting post #26 where TaxanJohn links to
which shows what is possible with the right pressure sensing equipment.
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  • #6
Darren, firstly welcome to the board. You seem like you're going to fit in just perfectly here! Since you introduced yourself, I'll tell you that I'm a development engineer working for a Diesel engine manufacturer, and have a lot of interest in biodiesel, and that your work sounds rather interesting.

Kistler are the people to approach for your instrumented injector/glow plug, allowing you to read in-cylinder temperatures. I believe you'll only be looking at a few hundred pounds for such a transducer; the real cost will be the high-speed data capture unit needed to record your results. Obviously you'll need to measure crank angle simultaneously so that your pressure trace is meaningful. I think you'd be foolish not to have some kind of detonation protection (or at least sensor) on the engine too if you're going to be doing that much development work.

As you probably know, combustion pressure traces are an extremely useful way of seeing what's going on in your combustion, but I'm wondering what you're actually wanting to prove out with your measurements?

An old mechanical engine like yours really shouldn't have any problem running on high biodiesel mixes, I doubt you'd even have too any problems on B100. What changes are within your scope that you can make to the engine? Injection pressures? Bowl shape? Turbo match?
  • #7
Hello Brewnog,

Sounds like an interesting job. Is the biodiesel interest professional or personal?

I found Kistler, Optrand and Piezocryst with a web search. I guess you recommend Kistlers product?

I've got a data aq. device that can stream at 50khz, which I'm hoping will do the job. Reasonable price also...

Sorry... detonation protection? What are you referring to? I thought that was a petrol / gas problem??

The fuel I'm using is not biodiesel. But pure rapeseed oil. - from a report I wrote a few years back details the basics (needs a good update) but I am aiming to optimise engines to run on vegetable oil only, cold starts and all (as detailed at [Broken]. I want to provide more evidence that this can be done sucessfully and provide an outline of the methods I use in optimisation so others can do likewise, also get a idea of the way different engines/fuel injection equipment behave when running this fuel. I also have a Skoda tdi that will be next on the list... Then there is the diesel motorbike...
Pure plant oils (aka PPO, straight vegetable oil;SVO) due to it's chemistry tends to inject and burn in a slightly different fashion to diesel fuel.

On the Mercedes (which is an indirect injection engine) I'm considering changing

injector pressures -currently it has 2 month old nozzles set slightly above spec

injector nozzle - I have a choice of 4 or 5 different types which have been used by others in this or similar mercedes engines either as standard fitment or experimentally.

glow plug protrusion length and glow plug control - to aid cold start and cold running.

Heating fuel with a coolant heat exchanger then possibly electric heat on the high pressure injector pipes?

Injector timing

Any thoughts comments?


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