I think my first example was not getting very close to what you actually want. Try this instead. It's also a bit weird, tricky, and not robust but the output seems right this time and it's semi-automatic for finding key, value pairs.

use warnings;
use strict;
use XML::LibXML;

sub snipName  { s/\s+//g and $_ = lcfirst($_) for @_ };
sub snipValue { s/\A\s+|\s+\z//g for @_ };

my $parser = XML::LibXML->new();
$parser->keep_blanks(0);
# $parser->recover_silently(1); # Might need, might not.
my $doc = $parser->parse_html_fh(\*DATA);

my $xml = XML::LibXML::Document->new();

my $root_name = [ $doc->findnodes('//div[@class="spec_section"]//div[c
+ontains(@class,"spec_row_header")]') ]->[0]->textContent;
snipName($root_name);
$xml->setDocumentElement( $xml->createElement($root_name) );

for my $col ( $doc->findnodes('//div[@class="spec_row_left"]') )
{
    snipName( my $name = $col->textContent );
    my $tag = $xml->createElement($name);
    my $value = [ $col->parentNode->findnodes('div[@class="spec_row_ri
+ght"]') ]->[0]->textContent;
    snipValue( $value );
    $tag->appendChild( $xml->createTextNode( $value ) );
    $xml->getDocumentElement->appendChild($tag);
}

print $xml->serialize(1);

__DATA__
<div class="spec_section">
              <div class="spec_row">
                <div class="spec_row_header orange_text_1">
                  Engine                </div>
              </div>
              <div class="spec_row">
                <div class="spec_row_left">
                  Type                </div>
                <div class="spec_row_right">
                  Diesel                 </div>
              </div>
              <div class="spec_row">
                <div class="spec_row_left">
                  Builder                </div>
                <div class="spec_row_right">
                  MTU                 </div>
              </div>
              <div class="spec_row">
                <div class="spec_row_left">
                  Model                </div>
                <div class="spec_row_right">
                  2x 16V396TB94                </div>
              </div>
              <div class="spec_row">
                <div class="spec_row_left">
                  Power                </div>
                <div class="spec_row_right">
                  2561kw / 3480hp                </div>
              </div>
              <div class="spec_row">
                <div class="spec_row_left">
                  Total Power                </div>
                <div class="spec_row_right">
                  5121kw / 6960hp                </div>
              </div>
              <div class="spec_row">
                <div class="spec_row_left">
                  Engine Propulsion                </div>
                <div class="spec_row_right">
                  Twin Screws                 </div>
              </div>
</div>
[download]

Which yields-

<?xml version="1.0"?>
<engine>
  <type>Diesel</type>
  <builder>MTU</builder>
  <model>2x 16V396TB94</model>
  <power>2561kw / 3480hp</power>
  <totalPower>5121kw / 6960hp</totalPower>
  <enginePropulsion>Twin Screws</enginePropulsion>
</engine>
[download]